Heres an awesome Deathknight bug.
Once you get lots of runic power, and runic strike procs, press it, but before you hit with it, dump ALL your runic power on DeathCoil, so theres no runic power left for runic strike, but since its pressed down when you had runic power for it, you will still cast runic strike even with 0 RP.
And no, it doesnt take the RP immediatly when you press it.
If that doesnt make sense, tell me, and ill make it clearer.
I forgot to mention, after you dump all your runic power, dont move, just wait for the next atack.