Hi,
I have been doing most of my research on vbulletin on the front end options. There are many options that vbulleting offers out of the box and there are many MODS(3rd party enhancements) written for it as well.
Vbulletin software can be found at vbulletin.com
Vbulletin MODS can be found at vbulletin.org (not .com)
Vbulletin is open source but they recommend you using the plugin system, if possible, to help ensure future compatibility with newer versions.
http://www.big-boards.com/statistics/
http://www.forummatrix.org/compare/phpBB+vBulletin
http://www.vbulletin.org/forum/showthread.php?t=176367
http://www.vbulletin.org/forum/showthread.php?t=177947
http://www.vbulletin.org/forum/showthread.php?t=181283
http://www.vbulletin.org/forum/showthread.php?t=176544
http://www.vbulletin.org/forum/showthread.php?t=171014
http://hardforum.com/
http://www.thepregnancyforum.com/
http://www.thepregnancyforum.com/