This may just be because I'm a minimalist, but I really dislike the big buttons and metallic like structures surrounding the border of the forum. A nice simple anything is always better in my opinion. However, that's once again, just my opinion.
@OP: I've always loved the OSDev forums (http://forum.osdev.org/
) primarily because they make excellent use of screen-real-estate. However, they're also using phpBB, so I assume that's just an option/theme somewhere.