A site with lots of test pages for style sheets: http://style.verso.com/boxacidtest/

Some more CSS: http://haughey.com/csshorrors/

The w3c CSS test suite: http://www.w3.org/Style/CSS/Test/

Some CSS2 tests: http://www.editions-eyrolles.com/livres/glazman/Tests/index.asp?ID=217554