Alessandro Fulciniti offers free CSS layouts on his site. All layouts use valid markup and CSS, and have been tested successfully on Internet Explorer/win 5.0, 5.5, 6 and beta 2 preview of version 7; Opera 8.5, Firefox 1.5 and Safari 2.
You can download his entire collection, 40 HTML pages in a single zip file.
(via superdeluxe)