TreeSize Free will help you to find what consumes your hard disk space by getting the sizes of folders and files inside your hard disk and display it in a tree like view. Once started, you don't have to do a thing, TreeSize will automatically gather all the needed information for you. You just need to tell TreeSize which hard disk partition to scan the next time you run it.
If you want a more graphical way in doing this, you can read my review on JDiskReport.
If you think that TreeSize Free will be just nice, download it from http://www.jam-software.com/freeware/index.shtml