Still no dice? Re-install MacKeeper (the demo version should do nicely), restart your computer, then uninstall MacKeeper using the procedure
here.
There's was only one item in my Keychain that I didn't recognize - and it's now gone - even though there was nothing to suggest it was related to MacKeeper.
I'll give this a shot before anything more drastic, although it seems curious that this issue would pop up "out of the blue". I certainly don't have any recollection of a MacKeeper installation, which would suggest it would have been quite a while back. Strange.