Topic: RailsForum.com -- very custom skin
This is my third or fourth PunBB installation, but the first I've felt the urge to really show off.
I feel like sort of a jerk making my first post on this forum in the "Show off" section, but I'm really proud of this skin.
The forum is for discussion on Ruby on Rails (I know it's ironic that I am using a PHP-based forum for a Ruby forum... but there just aren't any good Rails-based forum apps yet, and PunBB rocks so very hard). The skin gives the whole forum a very "Web 2.0" feel, I think.
It was skinned by Kelli Shaver.