MSI Afterburner is my choice for Overclocking.
I can give you some overclocking tips too :
- don't modify the core voltage
- don't touch the power limit
- add 50 MHz bumps on the Core Clock, after every bump run Furmark for 1 hour. (if you're getting artifacts, black screens , blue screens, 85+ degrees - LOWER YOUR FREQUENCY , until your GPU it's stable)
- add 50-100 MHz bumps on the Memory clock
Watch your temperatures with HWiNFO :
http://www.hwinfo.com/download.php - when you're reaching 85+ you should stop Overclocking.