WordPress Development Stack Exchange is a question and answer site for WordPress developers and administrators. It only takes a minute to sign up.
Sign up to join this community
What sites offer WordPress themes to download? (Can be paid-for or free)
It's community wiki so if we had one site per answer, and with a little additional detail on each site, what sort of themes they generally offer, whether their themes are paid-for or free etc.
http://wordpress.org/extend/themes
Official repository hosted by WordPress. Hosts several free themes and offers automatic updates.
ThemeForest hosts several premium themes for WordPress, Joomla, and other CMS platforms. They also sell a few standalone scripts. Check out the WordPress-specific category for just WP stuff, though.
http://www.smashingmagazine.com/tag/wordpress/
I like to use Smashing Magazine. While they don't have themes directly. They are constantly doing reviews on themes and even a Top 40 / Top 100 etc. The link above is the tag for Wordpress on their site, so you there will be a few other WP related articles, but a great source for some high quality themes.
Premium WordPress theme developers with a lot of stellar options. Just keep in mind that there's no one-off theme purchase option. A single fee will buy you 3 themes ... or you can subscribe by the month for multiple themes over that. Details are on their pricing page.
StudioPress offers the premium Genesis framework, along with several child themes.
Elegant Themes is a really good deal too, subscription-based but you get access to all his themes (and there are a lot of really nice ones)
Frugal is a highly flexible Premium Theme. It provides an admin interface with over 600 options for precise control over a site's Design, Performance & SEO. Frugal has a number of License Options ranging from $89-$499
Another premium theme resource that hosts themes for WordPress, Joomla, Drupal, and phpBB. The themes are high-quality, feature several customizable features, and sometimes come with multiple pre-set color scheme "skins." Membership is both time-based and entitlement-based (meaning you get a set number of theme downloads).
Press75 is mostly premium themes, but there are a few free ones in there too. Many are optimized for video content.
http://performancing.com/wordpress-themes/
Somewhat oldish, but clean and nice free themes.
Simplethemes has a couple of free themes, but offers mostly premium themes on a membership basis. Prices range from $39 for membership and includes access to a strong support community.
http://wordpress.org/extend/themes/commercial/
WordPress.org maintains a directory of Commercially Supported GPL Themes. Let me quote what they say about those themes...
While our directory is full of fantastic themes, sometimes people want to use something that they know has support behind it, and don't mind paying for that. Contrary to popular belief, GPL doesn't say that everything must be zero-cost, just that when you receive the software or theme that it not restrict your freedoms in how you use it.
With that in mind, here are a collection of folks who provide GPL themes with extra paid services available around them. Some of them you may pay for access, some of them are membership sites, some may give you the theme for zero-cost and just charge for support. What they all have in common is people behind them who support open source, WordPress, and its GPL license.
http://www.blogohblog.com/category/wordpress-themes/
Free themes (as well as premium). Don't know about current but older one were under CC license (for those who care).
It's a comprehensive collection of the best WordPress (premium and free) themes. You can browse, search and test drive over 800 themes form the most popular WP themes providers.
http://colorvila.com/category/themes/
It's a quality and affordable WordPress Theme Club.