The classic one to go for is Skinning+Leatherworking, which will give you access to Rogue-specialised armour and a variety of suitable armour-kits, along with the useful fur-lining enchant in WotLK.
Beyond that Enchanting is always a good one to choose, as (provided you have the mats) you can augment your own stuff pretty nicely, and later on sell enchants to other players. Enchanting is very money and resource-intensive, so I'd choose to pair it with either Tailoring (with which you can create masses of disenchantable items using materials you'll be gathering all the time anyway) or Skinning (which will provide you with some healthy stocks of leather to sell on the AH to supplement your income, along with the nice critical-strike bonus).
Mining+Jewelcrafting is also a very nice one to go for, as you'll be able to make decent rings at a level far below that which you'd normally acquire them, along with being able to create some useful BoP Trinkets later on and Gem-cutting beyond that, which is always a reliable money-maker and will save you alot of hassle end-game.
Mining + Engineering is great for using trinkets & such that opponents won't expect you to have. like fire or frost reflectors to knock back the PoM/Pyro mages or shadow reflector for locks/priests. bombs are also a good way to interrupt casters so you can keep them on lockdown.
Herbalism + Alchemy is also great cause you are a survivability class, so your pots won't go to waste. you can just vanish or gouge + sprint away to save the long time you have on them. you also get a double time boost while being an alchemist on the timers.