Simon Elliot told me that Ctrl-Scroll Wheel (or Ctrl-Two Finger Track Pad) Zooms the entire screen. Once it's zoomed you can move the mouse around and it scrolls the now larger image. If I ever sit at my computer and forget my glasses I can zoom this thing so large that Mr. Magoo could easily read it.
An anonymous poster mentioned that I could instantly put my Mac to sleep by pressing Command-Option-Eject. Sure enough, instant black screen. If you have ever wanted your Mac to act like it has narcolepsy, press that key combination.
Turning a Positive into a Negative
Karl C. brought up this gem: Press Command-Option-Control-8. It immediately turns your screen into a negative image. It reverses all of the pixel colors so that black becomes white and white becomes black. It can also be done through System Preferences. Karl said it's designed to help save power but I say it's designed to do to someone's machine that they leave unattended.
Slow Motion Exposé and Spaces
Karl also told me that holding down the Shift key while activating Spaces or Exposé would make the animation work in s-l-o-w m-o-t-i-o-n. Cool to know but not something I see using much.
The MacBook I have creates a disk image when you put it to sleep, slowing down the time it takes to fully go to sleep. Hendrik pointed out this post from MacWorld that will modify that feature using Terminal. Not to be outdone, an Anonymous poster mentioned that SmartSleep can be added to your Preferences pane to make the change without involving Terminal.
Mr. Clean to the Rescue
A couple of people mentioned that Mr. Clean works wonders on the white surface of the MacBook. Mr. Clean Magic Eraser was also recommended. Reportedly my MacBook will be "looking like new in minutes".
There you have it - some interesting little tricks. Got a really cool one you don't think anyone knows?