What software can I use to monitor how much of the graphics card is used when I run a certain application? I want to see how much my application uses the GPU
Also try
Rivatuner - http://www.guru3d.com/category/rivatuner/
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. RivaTuner supports all NVIDIA display adapters starting from Riva TNT family up to the latest GeForce 7 series and widest range of NVIDIA drivers starting from the oldest Detonator 2.08 up to the newest ForceWare drivers family.