Talents

I figure if I am going to provide all manner of information, I'd start at the basics, the talents, and build up from there.

The Elitist Jerks forum for DK tanking goes into detail for raiding, but leaves the heroic DK tank in the dust:

Discussion here should be on DK endgame raid tanking, both 10 and 25-man, biased to progression tanking (as opposed to taking a more casual attitude to your tanking role).

As I'm sure the raiding DK tank can read through that and follow that, I want to focus more on us bloody tanks who stick with Heroics.
I will split this out into three parts for the Blood tree, and then another for Frost/Unholy, and once I'm done I will combine them into a one-page guide for easy reference.

Tier 1
In the first tier we have one mandatory talent, Blade Barrier. You want this, and you want to keep your Blood Runes on cooldown all the time. Use Heart Strike or Rune Tap if it's available and you're not at 100% health. 6% damage reduction is nothing to sneeze at, and there is no cooldown on this aside from runes refreshing. With practice you should be able to keep this buff up 90% of the time.

To get to the next tier, we have two more options, Butchery and Bladed Armor. Butchery is pretty useless, even in fast paced heroics. The runic power regeneration (2 per 5 seconds) means it would take you one minute and 15 seconds to get one free Rune Strike. Gaining 10 RP after killing an enemy, especially on trash packs, could mean you start the next fight off with full RP, but it builds up fast enough normally that this talent has very little value.

Bladed Armor gives us 6 Attack Power for every 180 armor we have, which is a nice synergy for a tank. We get as much armor as we can, which gives us more AP, which in turn helps our DPS and implicitly our threat. Go ahead and put 3 points in there to get to the next level.

Tier 2
Here we find Improved Blood Tap, reducing the cooldown of Blood Tap from 60 seconds to 30 seconds. Blood Tap will refresh one of our Blood Runes as a Death Rune and Activate it immediately. Useful in a pinch to fire off a Rune Tap if it's available, or a Death Strike if there's another Frost, Unholy or Death Rune. Well worth spending two points on. (Though thoughts on this talent are mixed, and you will find many Blood tanks who do not have this. If this is not something you use, you could skip out on this talent)

Next up is Scent of Blood, which allows our melee swings to generate Runic Power. Dodging and Parrying is what we do for a living, or at least try to do as often as possible. There is some discussion around how many points to put in here, but most settle on 2 points. It should be up often enough to gain maximum efficiency from two melee hits rather than three. If you feel you are short on Runic Power, or that your Dodge/Parry is on the low side (below 20% combined), you could put a third point in here.

Scarlet Fever is our next option, and well worth investing in for Heroics where we can't always count on others to provide this debuff (Warlock, Warrior, Hunter pet (Bear, Carrion bird)). I will go into trash packs later (where we can tank diseaseless), but for the boss, taking 10% less damage is a must. So keep that Plague Strike up on the boss.

Lastly there is Hand of Doom, reducing Strangulate cooldown. I don't know any Blood DK that would spec into this. The reduction is from 2 to 1 minutes, so it's still a hefty cooldown for a ranged interrupt/silence, in addition to it costing a Blood Rune. Mind Freeze, with a 10 second cooldown, is our main interrupt, which suffices most of our Heroic needs.
I must say that on occasion (High Priestess Azil in The Stonecore's Force Grip) a ranged interrupt could be useful. But not enough to spend two talent points on.

I'll move on to Tier 3 and 4 next time. If you have any comments or suggestions so far, let me know.