By Corey on May 12, 2010. Updated: Mar 11, 2011.
Check out http://caniuse.com/ for a nicely designed interactive cross-browser compatibility chart. As a web developer I'm constantly wondering what HTML features are safe to use such that my sites render properly in all popular web browsers. This site makes it quick and easy to determine what level of support each of the major web browsers have for various modern CSS and HTML features.