Just curious what forum software people use for their websites, and what you find to be the best?
phpbb or vbulletin
I am using phpbb for 9 years and no problems. 3.0 + seo mod is quite good sollution, you can have it online in 20 minutes.
I use SMF (simplemachines.org), which on my site currently handles 400,000 visitors a month at around 6 million page views. I’ve used it and its predecessor(YabbSE) since December 2002.
I was also on the SMF team for a number of years as a support tech and also their marketing director - so I suppose I am a bit biased 
My opinion would be
Commercial : IPB (Invision Power Board), VBulletin
OSS : phpbb, fluxbb
Thanks all, I have done a bit of research and it looks like it is between VBulletin and phpbb
+1 on Simple Machines Forum. We used it as a forum for our online game and it worked without problems. Plus the plugin system is nice, we allowed embedding of youtube videos with a simple install of a plugin.
I like MyBB. It’s much better to administrate than phpbb.