I have IMatch - it's windows only. I like it because you get a folder view and a category (or keywords view). It also has a better "relocate" command - if you move your stuff outside of IMatch you can open it and then tell it where to look, and it's pretty good about relinking everything, where as the Elements Organizer has trouble with that. It also has scripting - and someone wrote a script to create a pure HTML gallery for uploading to a website, where as the latest version of PSE's Organizer uses Flash for the website generation.

There is a 30 day free trial for IMatch, and the next version (3.6) should be out very soon.

-Trish