There are quite a few places where you can download quality CSS and HTML templates/themes/designs for use on your website.

Nuvio
Rambling Soul’s Free CSS Templates
FreeCSSTemplates.org
Studio7designs
Andreas Viklund templates
Solucija CSS Templates
The Open Design Community
Template World
Styleshout.com
Zymic
free-css-templates.com

More Resources:

Top 14 Open Source Web Template Sites
Lifehacker’s Free CSS/HTML template roundup
30+ Free Three-Column Website Templates
Open Source Web Design

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