JDiskReport is a nifty freeware tool that will analyze your HD and tell you where all your diskspace is going.  With the proliferation of large hard drives it’s easy to leave large files around w/o even realizing it.  The tool is completely ad and nag free.  Being Java based, you’ll have to install JRE first.

Check it out: http://www.jgoodies.com/freeware/jdiskreport/index.html