http://www.pcbboard.com/cgi-bin/YaBB/YaBB.cgi
I'm thinking of replacing the iB with this as it seems like it could be better and like iB it is free.
So pay a visit, register and tell me what you think. Don't forget to bookmark it too in case UBB mucks up for some reason as it is more sensitive to permissions than YaBB (Yet Another Bulletin Board).