Music files may not be the primary space hog on your system. Perhaps you have a folder (or several folders) containing tons of random files, some of which may be needed. Folder Axe (free) can make short work of any such gigantic folder by splitting it into multiple subfolders according to several criteria. Once you've divided your folders, you can conquer them by moving through each subfolder, handling each file (or file type) as needed.
If you're unsure what is filling up your precious hard-drive space, WinDirStat (free) may hold the answer. This free utility uses a novel visualization method called treemapping to identify what files and directories are taking up disk space and how much of it they are claiming. The maps show files as pretty rectangles, color-coded by file type, in sizes that reflect the amount of space each occupies. Hovering over a rectangle shows you the file in question, and you can delete storage-space gluttons from within WinDirStat.
Cleaning your hard drive doesn't have to be an arduous, manual process. Instead, you can use Digital Janitor (free) to periodically move or delete files that meet certain criteria within a folder, such as "delete all EXE files from my Downloads folder."
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.