Some useful stuff I’ve recently added to my Emacs config (which I should really get around to moving to github already…):
FlymakeCSS explains how to hook up Flymake with a local copy of the W3C CSS validator to give on-the-fly syntax checking (with color highlighting for errors) for your CSS files. The utility of this isn’t as great as doing the same thing for your code (which Flymake can also do, of course), but it’s pretty cool, and not that hard.
Finally, the AutoIndentation page on the EmacsWiki has a couple of tips about configuring Emacs to correctly and automatically re-indent pasted code. This is extremely useful.