GPU-Z is a must-have Windows utility if you are using a NVIDIA or ATI graphics card. Much like CPU-Z, almost every last interesting detail of your graphics card is displayed. Hover your mouse cursor over any detail and a helpful popup is displayed with information on that detail.
CUDA or OpenCL programmers might find the details in the Sensors tab useful. It displays the GPU load and memory usage in real-time.
Tried with: GPU-Z 0.5.1