Post Nuke PnphpBB and phpBB are all quite tacky, I think. Invision is too. vBulletin is the only reasonable PHP Bulletin Board out there.

ASPPlayground is a classic piece of kit. Great ASPX Board if you're into that sort of thing. I would use it - but I don't have my Windows Server brought yet so I can't anyway. Don't ever believe Mono-ASP will ever work. It is dreadful.