Open Hardware Monitor (OHM) is a free open source utility that monitors temperature sensors, fan speeds, voltages, load and clock speeds of the different components of a PC (CPU, HDD, GPU, etc.).
OHM can be seen as the open source version of HWMonitor!
OHM runs on Microsoft Windows with the .NET Framework version 2.0 and above. On Linux systems the Open Hardware Monitor
Graphics card seems to be well supported: OHM has found my GTX 460 and my GT 240 and displays all information such as GPU usage, clocks or temperatures.