I just noticed Windows 7 (if it's Windows 7 you are using) built-in search has limited ability to do this as well. From Explorer click in the search box at the top right and you will see a listing for "Date modified:" and "Size:". Click on "Size:" to select the range of file sizes you want to search for.
WinDirStat - This app has a nice GUI for showing you where your space is going.