Anything that runs the CPU at 100% will heat up the CPU. Looping some Quake3 demos (or any other stressful FPS type game) for 15-20 minutes will heat up the insides of your case too.
I'd run any distributed computing client like RC5, SETI, etc., Prime95, 3dMark2kSE, and any Q3 or newer FPS game.
Even though some of those benchmarks stress your graphics card along with your processor, any combination of those benchmarks will put a full load on your system and heat it up in a worst case scenario. Let RC5 or SETI run while running Prime95's torture test and all your games.
Gaidin