NVIDIA Inspector!

A powerful overclocking tool for your graphics card, which also includes screen capture and video capture tools, plus overlays. Has a lower FPS hit than Fraps, and offers the same functionality. The beta versions include audio streams alongside the video capture.

RivaTuner is a complete powerful tweaking environment, providing you everything you may need to tune NVIDIA GPU based display adapters. The widest driver-level Direct3D / OpenGL and system tuning options, flexible profiling system allowing to make custom settings on per-application basis, both driver-level and low-level hardware access modes, unique diagnostic and realtime hardware monitoring features and exclusive power user oriented tools like built-in registry editor and patch script engine make RivaTuner's feature set absolutely unmatched. »

AgaueEye is a free hardware monitor for Windows, you can see your CPU/GPU/MB/HDD/RAM state in desktop or overclock your GPU, AgaueEye also support in-game overlay for popular games, so you can monitor the hardware state in games(over 3000 games supported now), then inspect the performance.