This is the spec I'm using:
http://www.wowhead.com/?talent=j0EMcZ0xZfg0hhckgcoMckut

Unholy Tank, but also puts out some decent DPS.

I keep my abilities fairly spread out, the only real macro I use for the DK is a Scourge Strike/Death Strike macro.
#showspellbyname Scourge Strike
/startattack
/cast Blood Fury
/cast [nomod] Scourge Strike
/cast [mod] Death Strike

Since I do tank/dps in raids I like to have my abilities spread out where I can get to anything/everything when I need to. My pull starts with Icy Touch (unless there's casters, then it's Death Grip/Strangulate). When mobs get in range, I hit them with Plague Strike followed by Scourge Strike spam (same button as lightning bolt macros on my Shamans). SS is great, because it generates Runic Power. Depending on the size of the pull, you should start spreading dots Pestilence, then Blood Boil, this should ensure you have aggro. If you've got a lot of mobs, you can do DND and Unholy Blight. Generally though, I don't bother. Just Pestilence my dots, and SS/Coil it till it's dead.