Well ... I'm still new around here... and also have lot to discover.
I've got a DK lvl 71 ... and I'm actually looking for a bunch of good infos to help me out. At the moment I'm spec as Blood/Frost DPS - Non tank. ( http://www.wowhead.com/?talent=jfVMqIcIsbMtzAZG ) <--- spec link (acutal lvl 71 spec w/ 2pts left to add)
So right now that's all good for lvling and survivibility. But I won't be lvling forever ... and that's all bout it.
Does anybody has a good spec for DPS/Raid @ lvl 80 ? And a few tips so I don't hang myself to reach the end ?
Pretty much all 3 of the trees are viable for raid DPS at level 80, from my personal experience Unholy still seems to be the most powerful right now, the usual Unholy dps spec looks something along the lines of - http://www.wowhead.com/?talent=jfVMVZZfM0Gtckxcq0csut you can switch some small talents around depending on your gear/playstyle/circumstance, such as picking up virulence if your hit is quite low, you can also pick up Anti-Magic Zone or Unholy Aura if your raid needs it.
For levelling, I would also suggest trying Unholy, due to the fact that DK's are quite capable of taking on 4-5 mobs per time whilst questing/levelling and Unholy is great for AoE. Taking your current level as a guide, you could try this spec now http://www.wowhead.com/?talent=jfVZZfM0htfoxcq0csup it's rather similar to the high end raid spec with a couple points sacrificed from blood and a couple of switches in the unholy tree, namely "On a Pale Horse" which is a great levelling talent due to the amount of time you spend riding about whilst levelling.
Of course these are quite opinion based and you may find that these specs do not benefit you so give all the specs a decent try if you can and see which fits your playstyle. For more information I would recommend checking out the armory of DK's of top guilds to see what conclusions they have come too and also check out the DK sub-section at Elitist Jerks for a more detailed analysis.