Utilities: DiskviewA very handy, very well-made utility is Diskview by Vyooh. The utility indexes your disks (local, removable, and network-attached) and simply summarizes the space usage information. The display is integrated into Windows Explorer app, so it feels very natural in MS Windows. That one piece of data -- amount of space a directory or a file take up -- helps tremendously in managing disk usage. Immediately one finds directories and utilities best compressed or even deleted taking up hundreds of magabytes, or even gigabytes of disk space.
Along with Beyond Compare this is the best windows utility I have stumbled upon in recent years.