Before you start OC'ing you'll need temp monitoring and stress testing software. PC Wizard 2008 and Coretemp 0.97 for temp monitoring and Prime95 (make sure it's the latest version) for stress testing to be sure your OC is stable. As for a good HSF, if you don't want to spend much money, then one of these two is perfect:
They are probably the best price to performance coolers currently available. However, if you want to do some extreme overclocking and don't mind spending $50, then this is for you: http://www.newegg.com/Product/Produc...82E16835118020
It is however more difficult to mount as it involves removing the mobo and installing a back plate. The other two simply use push pins. I am using the OCZ Vendetta ATM and I'm running at almost 3.5GHz at 37c idle and a safe 55c under load.