http://www.revouninstaller.com/ - revo uninstaller is basically an advanced uninstaller that cleans up the mess left behind by poorly written uninstaller programs. it'll check your registry and file system for bits left over, and it has a bunch of other features for tracking down and eliminating spyware as well.
http://aren.hulubulu.net/ - advanced renamer is the best free batch renaming program available. period. i used this extensively with a project a little while ago that involved over 1400 mp3 files, and it make my life SO much easier. the best part is the undo functionality, which will allow you to undo anything you've done since the program was opened last.
http://www.mp3tag.de/en/ mp3tag is the best free batch retagging program available. sensing a theme? i used it with the above project, and it is very powerful. supports tagging on everything, too, from common files like mp3 and wma to weird stuff like ape, optimfrog, and wavpack.
http://www.cutepdf.com/ cutepdf saved my butt in college more than once. it allows you to print to a pdf file, which is great for when you go to submit papers or need to print somewhere where they might not have office 2007 or whatever program you use. i'm sure most people have discovered something like this, but it works really well for proofing your papers before printing them.
what about you all? got any cool and useful programs that someone might want to try out?