There are thousands of theme developers for WordPress and most of their work
free for public use. They all use some specific repository to publish their themes.
The best source of themes and plug-ins is Codex. Let us look at the following URLs for themes:

• Codex at Using_Themes/Theme_List
• You will also find some themes developed by me at
  http://hasin.wordpress.com/my-wordpress-themes/
• If you want to develop themes, then the following URL is the best tutorial youcan have:custome themes at UrbanGiraffe To be informed about the arrival of new themes always visit the themes section in Codex and see the themes marked as new.