Nabthesis is a free bbpress theme by Nabtron.
This theme is simple and sleek design which can be used with wordpress and bbpress integrated if your wordpress installation is using thesis theme.
The theme provides same design and layout for your wordpress and bbpress installation so that your website and blog looks same!
Discussion page: http://nabtron.com/forum/topic/nabthesis-free-bbpress-theme
Download the theme from the link above
Unzip the theme in bb-templates directory
select the theme from the bbpress admin panel
Please change the header links (basic html knowledge needed) from the header.php of the theme.
Options page to change / add header links from the admin panel will be added in the future versions of this theme.
Please report any bug or issue related to the theme.