Rivatuner is one of the (if not the) best Tweak Utilities available for NVIDIA GeForce and ATI Radeon based videocards.

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.