I saw this question, but it seems to be directed toward Windows. What are some Mac demo programs that will really push a video card to it's limits?
4. If you have iTunes, the visualization modes would be good too.
An interesting story: An Incredible Mac Pro Demo: Takes Breath Away
Has a youtube link to a demo with 21 standard definition videos running at the same time.
The Spore site has Mac Trial demos for download.
Nowadays, to "push a video card to it's [sic] limits" has two different meanings.
For 3D-capabilities showcase, just grab the latest, bestest game demo. For now, I believe Call of Duty 4 will stress most machines. Even better, hook up a large external monitor and run it at max resolution.
For GPU processing showcase, I do not know of any program that taps on the new OpenCL APIs as of now, though you might want to give Quicktime X a shot at movie conversion. Rendering a movie with additional GPU processing on a Mac should speed up tremendously.
This said, these two will truly push the video card to its limits.