3DMark by Futuremark is the most well used benchmarking tool of the 3D performance of a computer. The ORB (Online Results Browser) allows you toÂÂ! easily upload and compare your score to the rest of the huge userbase. When your logged in, you can follow comparison links (like the one in my signature) to quickly rank your system against others.

3DMark05 is the newest, best for high end graphics cards.
3DMark03 is for the last generation or this generation's middle graphics cards.

Click here to go to Futuremark's website.