What are good trade skills for a hunter? This, like almost anything else in WoW, depends on what you want to do.
Do you want to raid and go for the best possible stats? Then Jewelcrafting + Blacksmithing is your choice.
Do you want to raid and be as self sufficient as you can? A combination of leatherworking, enchanting and Alchemy will be great.
Are you leveling, or just using your hunter to farm? Skinning + Mining or herbalism will be great.
Are you PvPing? then you might want to consider grabbing engineering for the extra tricks it has (even if half of em are nerfed in arena)
The standard is to have two gathering professions while leveling and two crafting professions for endgame.
This because the stat bonuses that crafting professions give are superior to gathering professions and thus will give you more dps.
Note that First Aid, Fishing, and Cooking are not technically trade skills, and do not count against your limit of two. All hunters should do First Aid. Fishing and Cooking help feed your pet, but aren't necessary as they can be a huge waste of time.
Check here for more detailed information on tradeskills.