You can get a program called
Fraps that`ll display the Frame Rate (FPS) in any 3D application and DVD/Video files. You make make short movies with it as well, make a log file, set the FPS display check interval, where abouts on the screen that fps is displayed, and a few other things.
I use this program alot, and its saves me remembering loads and loads of different commands to display the fps in various games.