GPU-Z is a lightweight utility designed to give you all information about your video card and GPU.

Main Features
Support NVIDIA and ATI cards
Displays adapter, GPU and display information
Displays overclock, default clocks and 3D clocks (if available)
Validation of results
No installation required
Support for Windows 2000 / XP / Vista (both 32 and 64 bit versions are supported)
BETA SOFTWARE - please test and post feedback in the forums