A List Apart: Practical CSS Layout Tips, Tricks and Techniques

Lots of good stuff on this site, but this article in particular goes over converting from tables to CSS, having left and right centered content in one row, abbreviations and making lists much more versatile. I used to read A List Apart with some frequency back when I spent far too much of my time writing web pages. If you’re just starting to look into things, Zeldman and Dean Allen really know their stuff. Those links are to their personal blogs, which I still enjoy when I chance upon them.