I used Treesize Pro, but despite what I said the last time Bitt brought up Scanner, I now prefer his program to Treesize. It's faster and has a cleaner interface, and most importantly it's free and doesn't give an annoying purchase message.

I do wish that Scanner had some features that Treesize had, though. A shell extension for one. I could go to a directory I knew had large files, and right click and get an idea of what was taking up what space. Scanner is just an executable, though, which is nice and compact. I also wish it had a little more information on the items it graphically displays. The window is so small, and it would be very easy to make an option that could double the size of the display, and add helpful info like percentages right onto the pie chart. Lastly, it would be nice to have the option to order the files on the pie chart in size order as well.