CSS2 Test Suite Failures Results: This is a great page on CSS support in the latest browsers. It has several dozen tests, explains how the browsers did, and lets you link to the live test so you can look at it in the browser you’re using.
It really shows you how CSS should work, if all browsers supported it uniformly. It irritates me to no end that Internet Explorer doesn’t support :first-child, content, adjacent siblings, min-width, and max-width. Infuriating.