For my mind mapping needs, I use the open source tool, Freeplane:
Freeplane is actually derived from another open source mind mapping application called Freemind. I think Freeplane is more end user ready at this point, though Freemind, when it is ready will allow real time collaboration on it's mind maps.
Neither product has the tight integration the Mindjet's products have with MS Office, but that's not really a requirement for me. Freeplane does everything I need in a Mind Mapping app, is free, and runs on Mac, Linux and Windows.