Folder Sizes
Folder Sizes is a free, open source program that is designed to scan your hard drive (C drive only at this time) and record how much space is used in every folder. The general goal is to make it easier for administrators, or just normal users, to see where the majority of hard-drive space is being used without having to right-click every folder and check manually.
The program has the unintentional side effect of letting parents have a fairly good idea where their spouses or children are stashing their adult material as well (as generally, they'd be larger in size, and in a hidden folder).
This program requires the .NET 2.0 framework. Only the executable file is included here. It requires no installation (although the .NET framework is a separate install in the even it's not currently on your computer), and is only 10K in size.
Folder names and sizes are stored to a filename in the same folder as the program itself resides.