Once your hard drive's house is in order, you may find that files you need to keep are filling up most of the drive, and perhaps--as is often the case for laptop users--you can't easily add hard drive space. In this case, a good compression utility may alleviate the problem. 7-Zip (free) is a fantastic open-source compression utility that can also serve as a file manager in a pinch. It can pack and unpack a wide range of compression formats, including .zip, .tar, and .gzip, but its main claim to fame is its .7z compression format which boasts an excellent compression ratio (often better than .zip) and strong encryption. As an added bonus, Gmail does not look into .7z files, which means that you can zip and send executable files to Gmail addresses (something you can't do with .zip files).
No discussion of file management software would be complete without mentioning Oops!Backup ($37, 30-day free trial). This fantastic backup utility bills itself as a "time machine for Windows," and that's an apt description. Oops does double duty as a file management utility, because you can use it to selectively roll back a single file to a previous version, even if it's several months old. It's like having effortless versioning across your entire system.