Here's a quickie, but I showed this to Venkat, and it made his day, so chances are good that others don't know about this handy keyboard shortcut. I used to always rely on my PowerBook to go to sleep successfully when I close the lid. But every once in a blue moon, something doesn't work right, and I open my laptop bag to a red-hot laptop. I suspect that it's latch related (and several other folks have suggested that this was the case). Now, I've taken to putting my machine to sleep before closing the lid. There are of course a variety of ways to do that; my recent common one was to hit the power button, which gives you the shut-down options dialog, and sleep is one of them. That's what Venkat's been doing.
But I recently ran across a better combination: Apple-Alt-Eject provides instant sleep (the Eject key is the one that ejects CD's, just above the delete key). One keyboard chord, and I have a sleeping laptop. I love it when I can cut a 2-step process down to a single keychord!