KCleaner is a powerful tool that will help to uncover redundant and junk files that you can safely delete.
The program has a good understanding of the kinds of clutter that will be left all over your hard drive by assorted applications. So aside from the usual Windows and browser temporary files, KCleaner can clear caches relating to Java, ATI Drivers, Skype, Google Earth, QuickTime, Adobe Reader and many more.
And while this won't necessarily free up a huge amount of space, it does mean that KCleaner's results compare will with the competition. We tried CCleaner on a trial PC, and it found 2.4GB of redundant files, for instance; KCleaner uncovered 2.73GB.
The program is also very configurable. You're able to choose precisely which types of files it should delete, and there are options to scramble file names before deletion, and securely wipe them so they can't be recovered later.
And once KCleaner is set up as you'd like, it can be left to run in the background, automatically cleaning up redundant files on a regular basis.
Please note, KCleaner will by default try to install toolbars and other "extras". If you don't want this, pay very close attention during the setup process, and decline the various installations as they appear.
Note that this the portable version of KCleaner.