If you could clarify on too simple then we might be able to help you more.
Most of the programs use loops as a redundancy to test your card, 3dmark test a lot of aspects about your card and with the higher res it keeps your video card maxed out(no matter what video card you have on the consumer level). Most games have demos like Insidious said but for a looping program I have found nothing better to test my card then 3dmark.
Other things would just play games like giants, sacrifice, unreal tourny, q3, RTWC, or any other high graphics games at high res for a long time.