ATI Tool: http://www.techpowerup.com/atitool/ - for tuning and tweaking your ATI card
ATI Tray Tools: http://downloads.guru3d.com/download.php?det=733 - for tuning and tweaking your ATI card
Driver Cleaner: http://www.drivercleaner.net/ - for removing drivers
Powerstrip: http://downloads.guru3d.com/download.php?det=169 - for tweaking your display (most useful for custom resolutions/refresh rates)
Rage3D Tweak: http://www.rage3d.com/r3dtweak/ - for tuning and tweaking your ATI card
RivaTuner: http://downloads.guru3d.com/download.php?det=163 - for tuning and tweaking your ATI card



If you know of any other useful utilities, please post them here.