What's eating my disk space?

You've done a perfunctory cleaning of your documents folder, deleted half of your iTunes library and parted with some seldom-used applications, but your startup volume is still mysteriously filled to the brim. Fortunately, discovering whereabouts of the lurking files responsible for eating your drive space is a task made almost weirdly simple with a utility called WhatSize.

WhatSize - http://www.versiontracker.com/dyn/moreinfo/macosx/21149 - is a simple tool that allows the user to quickly measure the size in bytes of a given folder and all subfolders and files within it. You would be surprised at how many useless files might be laying around on your hard disks. The files and folders are automatically sorted by size, with the biggest sizes first. 

While the app is measuring a folder the user can browse the files within that folder and immediately see the size in bytes. Hidden files, cache files, directories will all show up with their corresponding size. This application is similar to the ancient NeXTSTEP, DarkForest. 

Once the measuring of a folder has ended the user can also view the information by filtering for particular file sizes or types. The user can also move unwanted files and folder in the corresponding Trash bin similar to the Finder's Delete button.

WhatSize provides you with a hierarchical listing of all the directories and files on the selected volume, organized by descending size. This makes it extremely easy to navigate through the largest folders and look for the largest files within those folders, quickly running through the entire list and plucking items that you find useless or are willing to erase to reclaim disk space. Items are even color coded; those above 1 MB in purple, those above 1 GB in red, etc. Why isn't this functionality built into the Finder?

There's also a great "Table View" function (accessible via the Tools menu) that allows you to filter files according to size or type criteria. For instance, you can display only files larger than 1 GB, or only files (and not folders) between 1 MB and 10 MB, etc.

Here's a very brief example of how this application can save you surprisingly high amounts of disk space: Suppose you installed the iLife '06 suite, but never use nor desire the use of GarageBand. You delete GarageBand from the /Applications directory, and reclaim a measly 100 MB or so. Little do you know, however, that a nearly 2 GB directory associated with GarageBand (in fact, named GarageBand is still loitering in the /Library/Application Support folder. With WhatSize, finding this space glutton is as easy as looking among the largest directories at the root level of your startup volume (one of which will, depending on your particular filesystem, likely be /Library) then looking among the largest directories therein, and so forth. Tunneling down the file-size rabbit hole has never been so straightforward.