Here's a break down for you (based on my opinion):
Enchanting - Can be a very lucrative trade, but the materials are expensive because you have to disenchant items to get your materials. The better the item, the better the materials.
Alchemy - Until you get to the recipes that are skill level 300 and above, there's not much money in brewing. The real money lies in the Herbalism because the more rare plants/herbs tend to sell very well in the AH. For instance, on my server (Antonidas), a stack of 20 Fellweed sell for about 20g and from what I understand, it can be found all over the place in Outland. So 15-30 minutes of picking can make you 15-20g per farming run.
Blacksmithing - First, you have to decide whether to be a weapon crafter or an armor crafter. Then you need to find the rare and exotic recipes in order to make things that sell well. (One of your first items that should sell well is the Moonsteel Broadsword because it is used in a quest and let's face it, people are lazy and/or impatient. Anyway, this recipe can be purchased at a vendor in Booty Bay.
Jewlcrafting - This may be the most lucrative business of all the trades. Rings and necklaces alone will fatten your pockets fast. Take Mining with jewelcrafting and you can prospect the ore you mine for jems. In addition, you really get some awesome stuff to make for yourself. I don't know of any other craft with such handy stuff (Maybe enchanting.)
Tailoring - The best paying part of this trade is when you can make the 14, 16 and 20+ slot bags. Though I have been told that you need an s-load of stuff for each one, so hopefully you will be associated with a generous guild.
Leatherworking - The best thing a leatherworker makes (and sells) are the Armor Reinforcement Kits. They add an armor bonus to any type of armor, beit cloth, leather, mail or plate.
Believe it or not, Fishing can be lucrative as well, simply because there are fish that are used in quests and in trade components.
Though there's not alot of money to be made in Cooking, Dragonbreath Chili alone is a reason for learning it up. Food that makes you breath fire (and do damage in the process.) Priceless!