Professions for a tank

Professions boost your tanking stats in different ways. There is no mandatory profession for a tank these days, but some are better suited than others.

I am listing the useful ones below, describing what each of them will contribute:

Jewelcrafting
* Up to three prismatic gems, which will give you 41 stamina each. Will also help to satisfy meta gem requirements. Three 41 stamina gems would be 51 stamina more than using three "normal" stamina gems.
* One of the best tanking trinkets out there: Monarch Crab. Stamina and on-use avoidance coupled with two sockets.

Blacksmithing
* Two extra sockets. This could give you 48 stamina, 32 dodge, 32 defense, or whatever combination.

Mining
* 50 stamina.

Enchanting
* Enchanting rings with 24 stamina each.

Leatherworking
* Fur lining on wrists worth 90 stamina. That is 50 more stamina than the normal stamina wrist enchant.

Alchemy
* A very nice stamina and avoidance trinket (Indestructible Alchemist Stone).

Inscription
* Better shoulder enchant (Master's Inscription of the Pinnacle). It's 32 dodge more than the Sons of Hodir one.

Engineering
* Glove enchants (800 armor).

As you can see, Blizzard seem to have balanced the professions so that they give about 50 stamina each. Some of the professions are more versatile than others.
The best combination is probably blacksmithing and jewelcrafting.

Personally I'm running with mining and blacksmithing, but that's just because that is what I have had since I started playing. A tank that could create his own armor, and also farm the mats for it just sounded "right". :)