Fraps is a realtime video capture and benchmarking program available from www.fraps.com which allows you to benchmark your PC whilst playing games (the best kind of benchmarking). It can show a visible counter of the frames per second you are currently running at, which allows you to see if your system is performing up to spec.
Fraps has the ability to take in-game screenshots as well as featuring a video capturing ability which allows you to record footage in game, you can then use this footage to critique your performances or just to simply upload footage of in game antics to YouTube or simalar sites.
Recently a feature of Fraps has improved the ability of benchmarkers everywhere, it has an ability to log the frametimes of the game you are playing, this allows you to see the actual time it takes for your graphics card to render a frame on screen which can help diagnose stuttering in game.
Once again, Fraps can be downloaded from www.fraps.com, for a full licence it currently costs £24.95