Internet Explorer 7
Well... not quite IE 7, but the next best thing for now. Dean Edwards has put together some neat-o scripting using IE's behaviour functionality to implement heaps of CSS 2 properties (attribute selectors, child and sibling selectors) and then some more.
The only downside seems to be the odd issue such as this one raised by Adrian Holovaty about the file size and location of the file (so as to help users get it from one central source, and thus have that cached for re-use later).
On the positive though, there's hope for the old crock of a browser yet. Even better, Dean says there's more to come.