NVIDIA GPU Temp for Windows

The description of NVIDIA GPU Temp - Play With New Friends

Keep An Eye On Your GPU As It Gets Hotter.NVIDIA GPU Temp is a widget that sits on the desktop and reports by-second GPU heat in degrees. The applet provides great overall accuracy for many Nvidia GPUs, but advanced GPUs such as the Quadro series will not work well (or even at all) with it. There's no way to configure it outside of what Windows itself can do, either.