Look into Tailoring, if you're interested in greens.

It uses cloth, which drops off of any humanoid type mob, so does not require its own gathering skill.

As far as producing items specifically to DE, tailoring is one of the best.
Once you get to Northrend, there's a chance to receive extra cloth as a Tailor.

It might be worthwhile going Tailor + Mining or Herbalism on the main.
The other gathering skill on a slave with Mappy so its readily visible.

Enchanting can be on any toon, the ring enchants is ok, but its mainly for DEing rewards, where the mats sell for more then vendoring the item, maybe 75% of the time.

Currently, Jewelcrafting then Blacksmithing (extra sockets) then Inscription (stronger shoulder enchants) are the most bonuses over other professions. In 3.2, Blizz is supposed to balance this, so the bonuses from professions are relatively close. Still, each class has their own needs so one will likely be at least slightly better then another, as far as an individual class is concerned.