usually I only implement a 3 column css layout. so let’s start with http://mashable.com/2007/10/11/free-3-column-web-templates/
… and of course my absolutelly new favorite: www.openwebdesign.org …hundreds, thousands, millions of great open source css web templates 😉
download free open source css templates: http://www.free-css.com/ (not everything’s free here, but this is the free templates section: http://www.free-css.com/free-css-templates/page1.php)
also here download free css templates: http://www.freecsstemplates.org/
top css templates, free: http://topcsstemplates.com/
open source web design: http://www.oswd.org/ actually my past favorite free css templates site, but is this site still beeing updated?
last but not least: http://www.smashingmagazine.com/2007/02/14/free-design-templates/