True, there is the Sysinternals Disk Usage utility, but it only reports usage for a single directory, which isn't terribly helpful when you need an overall picture.
Here are some solid third-party alternatives that are free for personal use:
Comprehensive multi-pane text display, but lacks helpful graphics. Explorer shell integration. No cleanup capability, just deletion. Print capability. No menus, just toolbars. Fast. Very good.
- TreeSize Free
Simple hybrid text and graphics view. Administrator mode. Threaded for speed, very fast. Print capability. Integrated update check. Limited, paid version more capable. Good.
Clone of Linux KDirStat for Windows. Small and efficient. Threaded for speed, fast. Useful (and colorful) "treemap" display. No Explorer shell integration, but can be hacked manually. Cleanup capability. No print capability, but can email report. Recommended.