There's a free useful program that allows you to see how many bytes are in each folder, so you can keep track of where your harddrive space is going to. Rather than right clicking each folder then clicking properties and waiting for it to scan all the files this program automatically lists the folder size.
I personally discovered adobe premier temp files using 1.6 gigs in some random folder, even after I had uninstalled it.
I don't know much about it because the official site is in german and I'm lazy to babelfish.
Some random Yahoo group is offering it. 0.o...
They have positions around the world.
Random wireless hacking site in an .edu.