THIS.

Abaddon is right. Especially when you're leveling your first toon, you should have two gathering professions. Mining is always safe choice since not only you have Blacksmithing, Engineering and Jewelcrafting depending on your ore and bars, but also you can smelt and vendor your picks if the AH prices drop too low. Herbalism usually is nice profit, with Inscription and Alchemy reliant on herbs, but I noticed the volumes traded on AH are generally lower than ore. Leathers from skinning tend to sell, but not at major profits until you hit Wrath content, unless your server has low population of levellers versus endgame players who tend to spend heavily when rerolling professions for bonuses.

Generally, the only exception to 2-gathering profs rule would be when the toon you level is a clothie. I am still in process of leveling a lock (71 now) and I generally noticed Tailoring has many items to offer which will be nice to use even when you level via dungeon finder. Still, expect more use from your professions only when you hit TBC/Wrath content, not in vanilla. I seriously hope this gets fixed in Cata.

You may also wish to take up blacksmithing if you have a platie about to enter Northrend, but this profession is notoriously expensive and prohibitively hard to level without access to mining. The bonus is well worth it in endgame, and Cobalt set (later augmented with Saronite set pieces) is an absolute MUST-HAVE for any aspiring tank who just hit 70, but sometimes getting relevant items crafted for you via 2.Trade is gonna be easier than getting the profession so you can craft these yourself.

All that being said, my tailor is actually a scribe, and a lock (clothie). Embroideries go well with private inscriptions and you get them sooner than Hodir rep regardless what you do :3