As far as thermal compound goes, AS5 is the undisputed champion of the world. (I don't use it, but that's only because i've got a tube of Akasa AK-450, which is almost, but not quite, as good)
As far as cleaning the old compound off goes, every techie, techie website, and PC-World-know-nothing says "You MUST use isopropyl alchohol to clean thermal compound!". I have survived this far using spit and toilet roll.
My Opteron is overclocked by almost 50%, my idle temps never reach 35C, and I've yet to see 56C under heavy load. (but then, the arctic 64 pro might help!)
I'm not saying you shouldn't use isopropyl alchohol to clean your 'sink, but i've never had a problem using good ol' spit and a rag.
Not arguing with anyone, just my experience.
Don't ask questions, just click my rep tick. Now.