(Now: edited for more accuracy, re: tailoring!!)
I don't know, but stay away from woodcutting!!!!!!!!
Har har har har!! *bah-dum CHH* Thank you, thank you.
Ok, no, but seriously. I've been thinking about this a lot, whether I should switch up my professions. Right now I have alchemy and herbalism - a good combination, PLUS, picking herbs in flight form is OP. =P But the bonus from jewelcrafting is amazing, as is the blacksmithing bonus (more sockets ftw!). However, are they worse/the same/better than mixology? Better than being able to fund my own alchemy? How expensive is each profession, and what is the benefit, especially in regards to resto druids?
Let's look at the gathering professions first. Note that I got all my Auction House prices from either my own experiences with the AH, or through wowecon. Hopefully the numbers are somewhat accurate.
Herbalism: Herbalism lets you gather herbs that can be used in Inscription, Alchemy, or to be sold on the AH. Prices of herbs flucuate just like anything else on the AH, but typically a stack of 20 Northrend herbs will sell between 20g and 50g.
Herbalism also gives you Lifeblood, which I rarely used until I macroed it to Barkskin. As a healing class, I find it to be pretty redundant. Why use Lifeblood when I can just put one Lifebloom on myself for pretty much the same amount of healing in the same amount of time? Granted, it doesn't cost any mana, so that's nice. And it's great in arenas when you want every ounce of health you can get.
Skinning: Skinning lets you gather the hides or scales of mobs that you kill. They can be used in Leatherworking, Tailoring, or even some Blacksmithing recipes. Mobs in Northrend drop Borean Leather or Borean Leather Scraps. Five leather scraps can be put together to make one borean leather, and six borean leathers can be put together to make one Heavy Borean Leather. You can sell a stack of 20 Heavy Borean Leather for between 70g and 130g, depending.
Skinning also gives you a passive crit increase with Master of Anatomy, which will give you about a 0.7% crit increase. This makes it a good profession for some classes, but not the best for resto druids.
Mining: Lets you loot mining nodes that can contain ore, precious gems (uncut), etc. These can be used in Blacksmithing, Engineering, and Jewelcrafting. Different ore and gems sell for a wide range of prices on the AH.
Mining also gives you Toughness, which is pretty useless for trees. Tanks might like it, but we have no real use for it.
And now for the professions that will actually cost you money, not just time, to level. Note that I looked at these from an 'increase-your-spellpower' point of view.
Alchemy: Alchemy lets you make potions, flasks, and elixirs. You need herbs and vials to make these. Any and all players who are raiding anything that's not yet on farm should be using flasks or elixirs. At least, that's my opinion. I also happen to be a ridiculous min/maxer.
Alchemy also gives you Mixology, which increases the effect and duration of whatever you chug. Flasks that were one hour long are now two! Also, it increases the effect of flasks and elixirs by about 30%. Personally, I use Flask of the Frost Wyrm in raids, which gives me +125 spell power. With mixology, it gives me +162 spell power. So essentially, mixology is giving me more flasks and +37 spell power.
Inscription: Also uses herbs. You can make scrolls, glyphs, card decks, and a couple neat off-hands. I find that scrolls are pretty useless on 25 man raids, because you can't put most scrolls on top of all the buffs you get. In 5s and 10s, though, they're viable. And glyphs, depending on what kind they are, can sell anywhere from 10g to 100g on some servers - maybe even more. Prices will probably come down after more and more scribes discover more glyphs, though. Rare cards that you make for various decks can potentially sell for thousands of gold.
Scribes also get some great shoulder enchant options: the Master's Inscription of the Crag, or the Master's Inscription of the Storm. Right now I have the Son's of Hodir enchant which is +24 spell power and +6mp5. Changing to Inscription would give me +37 spell power. Interesting: it's the same as mixology.
You can also use Scrolls of Recall. This is a nice perk, but not important to increasing your healing output.
Enchanting: You can use this to enchant your gear or others' gear. You can also disenchant gear and use or sell the mats that you get. Abyss crystals typically sell for around 100g, and Greater Cosmis Essences sell between 10 and 15g. When leveling enchanting, you can only get mats by disenchanting gear, or buying them on the AH. It's not like you can go farm arcane dust like you can with herbs.
Enchanters get a bonus that lets them enchant their rings. Specifically, they're able to put a +19 spell power enchant on each one (there are other enchants such as stamina or attack power, but those don't apply to us). So this profession is a +38 increase to spell power. Same as inscription and mixology.
Blacksmithing: Blacksmithing is typically used by mail and plater wearers, so I've never really considered going with this profession. You can make some decent gear or weapons and sell it on the Auction House, but it's not like we can make ourselves items to use, due to our leather wearing limitations.
However, blacksmithing does give you the option to socket your gloves and bracers. Let's say you add two Runed Scarlet Rubies to those sockets, and bam, you've got an extra 38 spell power. See a trend here?
Engineering: Engineers can make a wide variety of random crap. They can make jumper cables to help rez the dead, repair bots for raids, random trinkets, and a MOTORCYCLE.
If you want to forgo the typical haste enchant on your cloak, you could opt in for a Springy Arachnoweave and increase your spell power by 18..... and that seems to be it. Am I missing something?
Tailoring: Tailors can make cloth gear and bags. 20+ slot bags can be sold for quite a lot of money on the Auction House. They can make sexy santa outfits, tuxedos and dresses! They can also make spellthread, which is an enchant to legs, giving you +50 spell power and +20 spirit (or +50 spell power and +30 stamina). This can be bought and sold on the AH. PLUS: a magic carpet mount!
The only special ability that tailors get is an embroidery to their cloak. The one we're interested in is the Darkglow Embroidery. It's got some nice mana regen there, but it's not enough to make me want to change my profession to tailoring. Tailors are also able to loot more cloth than usual off of humanoids, but again, this doesn't lead to raiding min/maxing.
EDIT: I forgot about Lightweave Embroidery! Bah! (Thanks Muffnman, for bringing this up!) Looks like this has a 45 second internal cooldown (like most procs) and has a 50% chance to proc once the CD is up. If it procs every 1.75 minutes, you will get an average of +39 spell power, which would make it on par with all the other professions. The question is, DOES it proc every 1.75 minutes? Or does it proc more than that? It should actually proc more than that - if it procs every 105 seconds, that means that after a cool down of 45 seconds, it takes over a MINUTE to proc again - which isn't accurate at all. So this embroidery is actually a bigger boost in spell power than other professions.
Leatherworking: You can use leatherworking to make gear, bags, ammo pouches, and armor kits. Resto druids should never be using leather armor kits, but low level ones are nice when leveling. Leatherworking obviously goes nicely with skinning.
Leatherworking also allows you to use Arctic Fur (looted from mobs by skinning them), which lets you make Fur Linings to 'enchant' your bracers. The enchant resto druids would be looking at would be Fur Lining - Spell Power, which boosts your spell power by a net gain of - you guessed it - 37 (The +67 would be in place of the +30 enchant you should already have).
Jewelcrafting: JCers can cut gems and make rings, necklaces, and trinkets. Once you have your skill maxed out, you can make quite a bit of money selling these items. The mining profession typically pairs well with JCing.
JCers have the benefit of cutting and using more powerful gems than the non-JCer. For instance, they can make Runed Dragon's Eyes, which are +32 spell power, rather than the normal +19 - an increase of +13. As a jewelcrafter, you can use up to 3 dragon eye gems. If you stick to straight spell power gems, this means a net increase of +39 spell power. Whaddya know. The other great thing is that these gems count for ANY color socket - which, as Najtrok nicely pointed out, will take care of your meta socket for you in one fell swoop. It'll also help you get some socket bonuses that you might previously not had.
So let's recap here:
Mining: +50 stam
Skinning: +32 crit rating
Alchemy: +37 spell power to Flask of the Frost Wyrm
Inscription: +38 spell power to shoulders
Enchanting: +38 spell power to rings
Blacksmithing: adds 2 sockets (so, +38 spell power to bracers/gloves with spell power gems)
Leatherworking: +37 spell power to bracers
Jewelcrafting: +39 spell power (if you go with the spell power gems), easily gained socket bonuses and meta reqs
Engineering: +18 spell power to cloak
Tailoring: chance to proc 300mp5 or chance to proc 250 spell power
So what's the best option here for resto druids?
Well, if you're going to take a gathering profession, I'd say take herbalism. Mining (+stamina) doesn't give you much a bonus to write home about, and skinning (+crit) is nice, but farming herbs in flight form is zomgeasymode, and takes the cake in my opinion. Also, Lifeblood really IS viable in PvP and PvE - you just have to work it in at the right moments.
However, if for some reason you don't want to take herbalism, your next best gathering profession (and a close second!) is skinning. Although restos don't use crit as much as, say, paladins, it's a still a nice stat to have, especially with Nourish being pushed into our repetoire of heals.
If you want to pair up that gathering profession with something else, you can choose any of the following: Alchemy, Inscription, Enchanting, Blacksmithing, or Leatherworking. Essentially, all of these have the *same exact* awesome factor. However, Jewelcrafting and Tailoring probably take the cake as the best non-gathering professions out there for restos. The only one that isn't on the list is engineering, although there are reasons why one might choose that as well (repair bots for the raid, for the win!).
Personally, based on limitations of funds, time, and still wanting to min/max as much as possible, I'd recommend one of these three combinations for resto druids:
Herbalism + Alchemy
Herbalism + Inscription
Skinning + Leatherworking
However, if you've got a ton of money, time, and want to get THE best boost, your best option is to choose jewelcrafting and tailoring. Joining these two will result in the best boost to spell power, provided you use the respective spell power options that each profession has to offer, plus you potentially fulfill more socket bonuses and you don't have to worry about your meta gem. You also loot more cloth off of humanoids! Booyah.
(Note however, that if your gems are already satisfying your meta gem requirement, and you're getting all the socket bonuses out of them, AND they were the exact gems you wanted in the first place, then JCing offers no other benefit over say, alchemy, or enchanting, or any other profession on that list. But typically Blizzard likes to make you choose - do you want to tweak your gems a bit to get the socket bonus? Or do you want to go with straight spell power and forgo the bonus? RARELY does Blizzard just put two red sockets on something, with a +spell power socket bonus. That would be too easy =P)
Readers: what do you all have for professions? Do you like your professions or are you thinking of leveling new ones?