good GUI on top of the trim command. simple, effective, no frills and free.
One window, drag application, done. No buttons to push, no icons. You can't batch operations (as Xslimmer does), but it is not a real problem after all.
start fast.
maybe some preferences about the language to keep would be a good feature.
if you want go the terminal route here is a good place to start
http://lipidity.com/apple/cleaning-apps-mac-os-x/