Rui CarmoXMind is a Java-based mindmap editor that has a few interesting features (such as Gantt charts) and a nice (if somewhat infuriatingly “social”) map sharing site associated with it.
Its only serious drawback is that it compounds the fact that it runs (or rather, crawls) under Java with an Eclipse-like look (which I hate), but it opens FreeMind files and looks vastly better than FreeMind on a Mac, so it has effectively replaced it for handling those as far as I’m concerned.