Getting to grips with the files and folders on your hard drive can be a chore, but the right tool makes it easier. WhatSize is a tool that combines the best of several disk visualisers into one package.
WhatSize scans your disk(s) and reports on the size of your files and folders with a straightforward, color coded, Finder-esque presentation. From there you can click through folders, drilling down to large problem areas, identifying files and folders was you go.
WhatSize can also give you a pie chart representation of your data with labels and concentric folder display. For instance, your home directory is held within the "Users" folder on the root of the drive, so the Users folder is displayed in the innermost ring, while your home directory is displayed on the next ring out. You can drill down by double clicking folders, or zoom out by double clicking on white space. It's simple and intuitive.
There's also a table view that you can sort by file size, or you can scan for duplicates, which scans and compares your files, which takes a while (read: hours) if you have lots of files, but then allows you to easily see what's doubled up. WhatSize will also let you scan files and folders with Administrator status, allowing you to scan other users data on your drive.
If you're looking for a comprehensive, simple disk space visualiser, WhatSize does the job admirably for US$12.99 and is available from whatsizemac.com. But don't take our word for it, download the free trial and give it a whirl.
Thanks to Klajd Deda for the suggestion.