Most of the time the only way to properly benchmark is to test your system in different high-end games, then compare your average FPS rate to other systems, or simply conclude that running Crysis at max-settings with a stable 60 FPS is probably pretty good.

Good benchmark games are some of the following:
Crysis
Unreal Tournament 3
Left 4 Dead
Portal/Team-Fortress 2/Half-Life2: Episode 2

These games utilize some of the industry's most frequently seen engines, such as Crytek 2, Unreal Engine 3.0, Source Left 4 Dead build and Source Episode 2 build.