If you're trying to squeeze a little more juice out of your Nvidia video card, consider nVidia Inspector (free). This overclocking package from Orbmu2K takes a different tack from older video card utilities, eschewing the system tray for a simple, extensible-pane interface that puts information and card controls front and center.
nVidia Inspector doesn't stay resident in memory once your changes are made. This straightforward approach means everything from driver options to crazy clock speeds are in easy reach, controlled by simple sliders.
Monitoring tools display a running graph of input from card sensors in real time; very useful when troubleshooting problems. If you like the sound of this, but are an AMD aficionado, look to AMD OverDrive instead.