I went with tailoring & enchanting.
Both allows you to upgrade your gear, as you level, without the need of instances. Quests, which are the fastest way to level, don't always give great rewards. However, having enchanting, allows you to disenchant most rewards, which can then be put to use as making your gear better.
Only having the 1 toon, I picked my professions carefully, thinking what 2 I would benefit the most from.
Don't forget that with tailoring you can make your lock a 32 slot shard bag, as well as other bags. They can also make a flying carpet. Granted you can get them from other users, I feel it's best to get the mats and make them yourself. Saves you gold.
I make decent gold with enchanting. I constantly see people asking for links to high level enchanting. Users usually pay me a 20g tip for an enchant.
Enchanting materials can be expensive, so I feel it's just easier to be able to enchant your own gear. Materials are fairly easy to come by.