I've ported the bbCode Plugin for Wordpress by Jeff Moore to bbPress, seems to work fine; not all the bbCode is marked up as it's not allowed by default with bbPress, I plan to fix that in version 0.2, but for now Enjoy !

Download bbCode Plugin for bbPress

Installation is simple in the current implementation of bbpress, just rename bbpress_bbcode.txt to bbpress_bbcode.php and place in your my-plugins directory (See bbpPress documentation for full details.)

This plugin has been tested on v0.75 & 1.0-Alpha so hopefully will work on anything in the middle.