The two HDD visualization tools that help me often are the

1.Space monger 1.4 (the last freeware version)

spacemonger

2. OverDisk

USAGE:

1. I can’t think of any other simple way to find the huge chunk of useless data in deep directories that are produced mysteriously.  eg: the replay.bpf (2GB) created by GRID PC game.

2. My computer is infected with a mysterious bug my anti-virus refuses to detect. It doesn’t let me un-hide my hidden files. These software help me by showing them in the map.

I personally prefer Space Monger than OverDisk probably because I’ve been using it for a long time now.