Download FolderSize
With a recent influx of video projects, I’m finding myself butting up against the capacity of my primary hard drive, which means I need to shuffle files off to on of the several external drives on my network. The trick is quickly finding which files and folders make the biggest impact on available space before moving, which is a hassle with the way Windows Explorer operates by default. For detailed system information, including growth over time and predictive resource consumption, I swear by Disk Triage. When I want quick information, I want to go straight to Windows Explorer and find large folders and move them to a new drive. For that task, I count on FolderSize, which replaces the standard Size column in the detail view of Windows Explorer. Instead of needing to right-click on a folder to view its properties, I can see the actual size of a folder in Windows Explorer, in context, with FolderSize installed. Sorting by size filters the big stuff to the top of the heap and my problem is solved quickly without any extra steps. [Windows 2k/XP $0.00]
Windows Explorer before FolderSize shows only file sizes in the size view.

Windows Explorer with FolderSize adds the Folder Size column, displaying sizes for both files and folders.