Hi,
demos [1] from the demoscene are pretty demanding and freely available stresstests, especially for everything 3D-related. The size-optimized productions (4KB, 64KB) might also exploit some lesser known side effects of bringing up a program. A review of running the most popular demos with wine 1.2-rc2 was recently posted here [2]. Out of 25, 14 are flawless and 4 OK - pretty good numbers IMO. (BTW the demos can be downloaded using the search function of the website.)
Regards,
Wolfram
[1] http://en.wikipedia.org/wiki/Demo_%28computer_programming%29 [2] http://pouet.net/topic.php?which=7400