http://windirstat.info/ <<< good but sunburst diagrams are way better; also it does not allow to navigate into folders.

http://w3.win.tue.nl/nl/onderzoek/on.../sequoiaview// <<< Does allow for filter-rules

http://www.steffengerlach.de/freeware/ <<<<< Scanner; liked that one. (Doesn't sort by formats though)

http://www.jgoodies.com/freeware/jdiskreport/ < junk xD