Press CMD-OPT-CTRL-8 and the colors on your screen will be inverted--white pixels turn black, blue turns orange, etc. This seemingly useless trick is actually an accessibility feature, and can be helpful in bright-light situations, but we all know it was really implemented to let geeks prank their unknowing friends.
2 of 5 Screenshot by Sharon Vaknin/CNET
Talk to me, Terminal
In Spotlight, type "Terminal" and hit Enter. Here, type "say" followed by a word or phrase. Useful? No. Awesome? Yes.
3 of 5 Screenshot by Sharon Vaknin/CNET
Hold the Shift key, then minimize to escape into a moment of life in slow motion.
4 of 5 Screenshot by Sharon Vaknin/CNET
Zoom in anywhere
Mouse over the part of the screen you want to magnify, then press option while scrolling up (two fingers up on the trackpad, or with the mouse scroll wheel).
5 of 5 Screenshot by Sharon Vaknin/CNET
Play retro games in Terminal
Go to Spotlight, type "Terminal" and hit Enter to launch it. Then type "emacs", and hit Enter. Once the new screen loads, hit Esc, then type "x" followed by "tetris," "snake," or "pong." Enjoy!