I know I run frost, and my tanking tends to go Icy Touch, Plague Strike, Pestilence, Blood Boil to infect and build aggro on a group, followed by strings of Howling Blast or Obliterate (depending on whether I'm building single target or multitarget threat) with Rune Strikes and Frost Strikes thrown in for good measure until the disease timer is up, at which point I reapply and continue.

Now this isn't remotely helpful for an unholy DK, as I haven't looked in to how they tank, but I thought I'd toss it out anyway.