FreshPress Themes – A site focused on providing fresh looking WordPress themes with an emphasis on CSS and XHTML structure.
Kickass Web Design – WordPress themes for download. Individual theme author. Custom work available for a fee.
New Dirt WordPress Themes – Free WordPress themes released under a GPL license and custom WordPress theme design.
Omni WordPress Theme – A site showcasing a premium highly-customizable WordPress theme.
Premium WordPress – A site that showcases free and premium WordPress themes. Also resources from premium sites of WordPress.
Simple WordPress Themes – WordPress theme site featuring third party themes. Each theme posted has a thumbnail preview, download link, and demo where available.
Themes Junction – A website with many free wordpress templates.
Themes Pack – A collection of free WordPress Themes from various styles.
Top WP Themes – Download quality and professionally designed WordPress templates for free. Also allows user ratings of themes.
Using Themes – The official WordPress codex help page for using themes.