I’m sure this will come as old-hat to everyone out there, but on the off-chance you’ve never seen it, I highly recommend checking out and playing around with the CSS Zen Garden. CSS Zen Garden is a demonstration of what is achievable through correctly separating your content from the accompanying presentation, and the results really are spectacular.

Dave Shea, creator of CSS Zen Garden, has also come out with a companion book, of sorts, The Zen of CSS Design.