like yourdeardaniel says, Shin-etsu thermal pad
if you are overclocking like crazy, scrape it off before you use it and use ArcticSilver5
if a mild or no overclock, the stock TIM is actually very effective
I even OCd with mine for a month or so, kept temps in check well
screwed myself in the process, cause the TIM melts into the heatsink and I had to lap the ah heck before I could use AS5
ah well, ya live and learn