Help finding an application that finds the largest files on your hard drive?

I used to use an application that was able to list every file/directory on my hard drive and list them in order of size. I edit large MP2 video files and sometimes it's hard to remember where they all live... this tool was useful because MP2 files are so large, they often are the biggest files on my machine.

Any ideas on how to find them?

 

GrandPerspective is exactly what I was looking for. Great job guys.