LightMe is a small Preference Pane and background daemon that allows you to change brightness and power of your monitor with customizable keyboard shortcut. Using Lightme you can reduce to a preset value the brightness, restore it to the last value (and with anther click of your restore shortcut you can switch to the max value) and poweroff the monitor. You can also hibernate your computer since 2.0!
Lightme core is a little lightweight background daemon compatible both with Intel and PPC processors. You can install it at login, activate or deactivate it with a simple click from the preferences pane.