Skinnalicious - Offers skins and themes for applications like Windows XP and Vista, Sysmetrix, and Rainlendar. Registration, free, is required to access most of the site.
Theme Jockey - Custom designs desktop themes for home and business.
Themes Heaven - Free themes for Windows Vista, XP, WordPress and cell phones. Writes on design related topics.
Themes.org - For the Linux and UNIX community. Categories include fantasy, science fiction and nature.
