if you are not going to overclock much i would suggest you get any cheap cooler master or arctic silver paste it will definitely be enough . however you also need to make sure you apply the thermal paste correctly so check some videos on youtube if you are not sure on that. some people prefer a thin layer of paste spread over the entire cpu surface and some may argue that a dab of paste on the center of cpu is best but do some research and chose the best method. no matter how good your thermal paste is it cant be useful unless applied correctly. i personally use the cooler master ice fusion and i have spread a thin layer of paste on my core 2 duo after overclocking it from 2.93ghz to 3.5ghz my core temps are still at 70c max even while playing games (metro 2033).
check out http://www.youtube.com/watch?v=fRRWbQUqW1Y