http://www.sixty-five.cc/sm/
Every once in a while I find an app which really makes me go wow - and then turns out to be useful too.. I highly recommend you give this a try; if you're anything like me then you've got 100's of mb's of cr@p you never even knew about on your hard drive..
It's a bit bewildering at first but it tracked down a few problems on various PCs for me (like I had over a GIG of firewall logfiles I didn't know about).