Basically, crafting makes you money proportional to the work you put into it. If you're like Breesy and you camp the auction house with savvy, you can make money pretty early on. If you're like me, you don't spend lots of time in major cities and you took your trade skills mostly for self-reliance-- and you don't make much money off your trade skills.
Gathering professions make money unless you're gathering the mats to have something made on commission. The crafting professions are harder to turn a profit in, but there are some things that go well. Every once in a while you'll find a recipe that has a specific use, like for a quest-- making those in small numbers can turn a fair profit. For example, the Frost Trap in Dire Maul requires frost oil. Obviously people won't need a full stack of frost oil if they're just running Dire Maul once, but put up one Oil at a time and you can do well. Specific items needed for quests, or for other tradeskills, can turn small but reliable profits.
For alchemy, most "normal" (healing and mana) potions go for the price of the materials-- but the more exotic stuff sells well. +agility potions sell like hotcakes, for example.
For blacksmiths, the really good dagger recipes can be very profitable, and some are available early on. Past that, it takes a long time to turn a profit.
Enchanting takes a LONG time to make money off of, but when you get your skill to 280+ and start getting the desirable recipes you can start recouping your investment.
Tailoring is pretty much for bags, but there are a few other things that can make money.
In leatherworking, armor kits sell surprisingly well and surprisingly consistently. They're also dirt-cheap to make. Again, don't sell full stacks; sell a few at a time.
Engineering is a money sink.
As a rule, production skills are loss-leaders-- you lose some money on them, but you always have a certain baseline of equipment/ bonuses you get out of it, and you can start making the really cool stuff late-game.