The final fight in Trial of the Crusader is the Traitor King, Anub'arak. We've all fallen through the floor by now. How do we DKs provide the pwnage? It's actually one of the more straightforward fights:
Pull: Just run in. Be a bit behind the tank so you don't get cleaved while the tank is turning him. Icy Touch while running in. Plague Strike. Regular dps rotation blah blah (we got it Hine). Get proc-buffed pets out and diseases rolling as per normal. IF you are on hard mode, you have to be stingy with your permafrost, so you'll likely be asked to Death Grip an orb to Anub's hip. The adds will be tanked here to allow aoe/cleave damage to take the adds down. When you get two adds, pestilence and Death and Decay to hit both them and the boss (or just pest and howling blast as frost). If adds are tanked seperately, usually just the ranged will dps them and melee stays on boss.
If you're not completely foolish with aggro on Anub, the biggest risk of dying here is not paying attention and getting hit by spikes in P2 or going totally nuts on adds in P2 and getting too many stacks of their acid drenched mandibles debuff.
Phase Two: Try to spread diseases to as many scarabs as possible. I find Death & Decay doesn't add much dps because the scarabs don't clump all that much and seem to constantly move out of the aoe area, but I will use it if I get three or more relatively stationary adds. Just dps them down.
Phase Three: As soon as the Leeching Swarm starts, your raid should go all out. Bloodlust/Heroism should be popped here. Use your potion of speed. Get your gargoyle/dancing rune weapon/ghoul out, and army of the dead. We let adds submerge, but they can still be tanked on a death-gripped frost patch on Anub's rear if you get more than one set. If you get too low, and aren't 100% sure of your healers, you can always Death Strike to get a little health back. A dead DK does no dps!
Heroic: If you're on heroic, the fight is much the same, but the health and damage of Anub is of course increased. You'll get double the Nerubian Burrowers (big adds), and of course, only 6 orbs for permafrost, basically two per phase one. Anub will need to be kited, so if you get chosen, you'll have to run! Switch to unholy presence if you don't have a speed enchant and get going! Anub picks up speed, so be careful. The kiting mechanic has been documented elsewhere and isn't specific to DK dps, so I'll leave it at that.
Your dps should be decent at least. If your raid groups the adds on Anub, you'll do very well since every spec does nice extra damage on those adds. On phase two however, we aren't extraordinary. Melee have to run all over, while ranged tend to be able to stay in one place a little more and pick their targets. You'll get cleave damage if you're blood, and tons of disease damage if you're unholy. On normal, my dps can be low - in the 6-7k range. If I can convince my guild to work more on clumping adds in both phases, it should jump up significantly.