I’m sorry but I honestly do not what’s out there in terms of plugins that offer this kind of functionality. BuddyPress is the only one I’m at all familiar with. The current BuddyPress requires specific theming for it to play well with your theme in most cases. However, their next big release, BuddyPress v1.7, which should be getting close, has an all new theme system that allows it to fit into WordPress themes in general a bit better.
Maybe you could try using the development version of BuddyPress 1.7? — http://buddypress.org/download/