FurMark reaches 99% fan on my stock EVGA 55nm 260 "SSC" edition (675MHz). Temp peaks at 86c and settles at 85c as the cooling fan speeds up quickly. I noticed that 640x480 heats up faster than higher resolutions.
Another good one is "OCCT 3.0" which will stress GPU and CPU same time. It's a killer, be careful. I measured absolutely insane wattage from my simple i7 + GTX260 setup. It has a custom cuda/gpu routine, and a tuned LinPack run for various CPUs. It makes Prime95 stress test look like child's play for power consumption.