One small feature worth a mention is that Disk Defrag supports Windows 7's superbar progress indicator. You can choose to defragment your entire drive or target specific files or folders. It's also got a number of other smart features, like free space consolidation and intelligent system file placement. Disk Defrag can also be set to run automatically when your system is idle.
The installable version can also clean up your temp files prior to defragging, minimize to the system tray, run scheduled jobs, and integrate into your right-click context menu.