XFX 9800 GTX Black Edition 512mb
Oblivion is a game that really taxed all of the cards at the time of its release. Well over a year on and the current generation of cards simply fly through it. However, with advanced HDR, excellent draw distances, detailed grass and scenery as well as fantastic water/magic effects it's a good game to gauge performance for those who love RPG's.
Company of Heroes is a WWII-based RTS game that has an enormous amount of world detail. I played a DirectX 10 patched version of the game that gives modern GPU's a bit of a workout.