D/E, Mining, or HerbFollow

All four each have their ups and downs. I figure that Skinning is the easiest of the four to skill up as well as the most consistent way of making money (leather prices don't change much).
Mining is profitable from the very first copper ore you dig up and is an excellent method of making cash for a new toon, not difficult to skill up but will likely take the most time to skill up of the gathering professions.
Herbs isn't very profitable until around 200 or so skill, but is well worth the effort.
Enchanting requires a considerably greater investment than the other three gathering professions to begin with, but once you get to 275 and up (and able to DE anything worthwhile in the AH) it isn't uncommon to spend 300-400g buying greens for DE that can yield 600-750 or more gold worth of mats. By adjusting the minimum profit values in Enchantrix slightly once you've gone past 125 enchanting you will yield more items that will likely yield reagents that you can use to skill up with, as well as scoring more higher level items. I'm not disclosing my present Enchantrix minimum values, but I will say that most of the items that come up are Outland greens, pre-BC 55+ greens, an occasional blue and lots of 40-50 level items.

In terms of time spent, how long does it take you to gather a stack of stranglekelp? Mining certainly makes more gold for two reasons: more professions need ore/bars than those that need herbs, and each node yields more mats, making gathering ore a bit easier. The drawback to mining is that it's harder to level, since there are many herbs that will help you level herbalism, but ore is restricted to only a few types, and there are largish gaps when it becomes tough.

If you are going to go with gathering skills, supplement your income by fishing. Making money through fishing is covered quite thoroughly in the FAQ.

Also, at high levels enchanting is fun (well, DISenchanting). You can solo-run old instances to d/e items. At level 70 I can make a few hundred gold running BRD a few times in an hour or two; sharding the items gives me at least 6 large and 10 small brilliant shards (probably more), along with trash, random greens, and recipes (Fiery = 60-80g).

It's a great tactic to use enchantrix to play the AH-d/eing game, then spend a few hours farming old instances, then come back and scan once more before logging off. I should have my epic flyer in a week or two.