http://openhardwaremonitor.org/
The Open Hardware Monitor is a free open source application that monitors temperature sensors, fan speeds, voltages, load and clock speeds of a computer. It supports most hardware monitoring chips found on todays mainboards like the ITE, Winbond and Fintek families. The CPU temperature can be monitored by reading the core temperature sensors of Intel and AMD processors. The sensors of ATI and Nvidia video cards as well as SMART hard drive temperature can be displayed. The Open Hardware Monitor runs on 32-bit and 64-bit Microsoft Windows operating systems without installation