Some tools I've found useful

[David_L6]

OCCT: http://www.ocbase.com/perestroika_en/

Core Temp: http://www.alcpu.com/CoreTemp/

CCleaner: http://www.ccleaner.com/

HijackThis: http://www.trendsecure.com/portal/en-US/tools/security_tools/hijackthis NOTE: Be careful when using this one.
http://en.wikipedia.org/wiki/HijackThis

IObit Smart Defrag: http://www.iobit.com/

SpeedFan: http://www.almico.com/speedfan.php