DDR like Ciaossu posted is good. I personally use MagicRunes. Whatever works for you, it's one of those classes where your resources just need to inform your decisions more than anything else, so having them center and readable is most important. I haven't played Unholy in literally years so I'm not sure I'm the best for current info there (I hated festerblight).
http://www.twitch.tv/theyanger/c/2509699 My UI so you can see what I'm talking about but:
The finer points of DK UI and ekeing out performance are basically just resource management/awareness. You can see my runes are dead center with my RP right next to it. Important CDs I have weak auras for directly below that, and it's all in line with the blizz proc UI making a nice little square around my toon. You don't have to do it like that obviously, but the principles are the same - the information you need to react to quickly, needs to be in your direct vision, not your peripheral. Blood Tap charges are in numerical form directly above that too, top left of my Target of Target.
Aside from setting up your UI, it's just a matter of getting used to what is important and when. AMS soaking and stuff for instance, treat it like a dps cooldown. I've modified some of what I track a bit since then. Diseases are to the right, more important as Unholy than as Frost.
The real trick is once you know which aspects you're not as good at tracking, those are the things you can emphasize on your UI. Example: I'm AWFUL at blood plague when I'm frost (at least obliterate frost, masterfrost it's a lot simpler), so I have an extra aura that screams at me when it falls off.
Soul Reaper is usually another trouble point, I had to make 6 seperate weak auras to track it correctly for all specs, but it's worth it - it's a HUGE part of your dps (especially as unholy) and it's a pain in the dick to use it well if you don't have something like that.