Whether for the PC, or the Mac, there are some great free utilities to help you keep your hard drive free of clutter.
When your hard drive fills up to the point where you need to clean it up, it's often hard to find exactly where those files are that take up so much space. These two programs give you a visual representation, making it easy to quickly remove files you no longer want or need.
There are many programs out there that provide these nice visual queues, but WinDirStat stands out due to it's mature stage of development, and it's price tag: $0.
WinDirStat gives you a file tree like you're used to, with percentages of space taken, and a reference to the total size of folders/files. When you click on a file (or a square in the visual area), you'll get loads of good information about the files location and size.
Like WinDirStat, GrandPerspective offers different sized squares. It's not quite as in-depth with a file tree as WinDirStat. However it still allows you to see your hard drive visually, then click on a square, discover what file or files are taking up all that space, and allow you to delete them.