ThemeForest | Premium WordPress Themes, Web Templates, Mobile Themes
Themeforest on the Envato Marketplace

ThemeForest.net

ThemeForest, and the entire Envato Marketplace family, has changed the way many build, access, and approach web construction, design, and extension. It’s a win-win, for users and designers, developers and owners.

In their words, you can begin your search for:

Site templates and themes to skin popular CMS products like WordPress, Drupal and Joomla, starting at $5.

It’s a great place to start for WordPress Themes, and I recommend it.