Ubuntu 9.04 comes with some visual effects from Compiz turned on by default. This post contains a list of the key combo’s used to active some of them. Compiz also offers many other “cool” effects. If you install the compizconfig settings manager you can enable/disable all of the neat effects (most of which are eye-candy, and not really useful).

Note: The “Super” key is typically labeled with a “Windows” logo on most keyboards.

Desktop:
Expo: Super-E will show all of your desktops at once, and you can drag windows from one to the other. Arrow keys allow you to select a particular desktop, and the enter key will zoom back to it.

Snapping Windows:
By default, as you move windows they will “snap” so that their edges are aligned. To disable this behaviour, hold the SHIFT key down when moving windows.

Scale Windows:
SHIFT-ALT- will go into “window picker” mode. Then you can use the other arrows to pick a window, and when you release the SHIFT-ALT modifier keys, that window will move to the front.

Desktop Wall:
Allows you to switch between desktops using the CTRL-ALT- keys (up/down/left/right).

Accessibility options:
Enhanced Desktop Zoom: Super-button 2 (typically, button2 is the middle button) will zoom in a LOT! Super + the scrollwheel (if you have one) will allow you to zoom in/out a bit less. If you would like to use the keyboard for zooming, you will need to install the CompizConfig Settings Manager and enable keyboard zooming.

Negate: Negate (black is white, white is black) a window or the whole screen. Super-n (window) or Super-m (screen). Useful for increasing the contrast of text, or just making people wonder what is wrong with their desktop.