I would highly recommend the Team at JFusion. They know what they're doing, they have a great product that is getting better everday with all of the community contributions, and they are quick to respond and support you with your needs!
They are going to be the first group to be able to pull off a seem less integration of Joomla 1.5.x, AEC (Account Expiration) and phpBB3. That will rock the Joomla! world.
Get involved, download JFusion.