Command-B toggles "Bold" on and off. This is one you have to know: I rate it up there with Command-Z, -X, -C, and -V. And -P.
Essential Mac Keyboard Shortcuts: ⌘-B for Bold
Introducing the One-Minute Macman blog
Providing daily (or almost daily) Mac hints, tips, and stories-- readable in one minute! By Christian Boyce.
How to find stuff on the Mac’s Desktop
Quickly find items on your desktop (or in any Finder window) by typing the first letter of the item. You don't have to search. Just type.
Essential Mac Keyboard Shortcuts: ⌘-I for Italics
Add Command-I to your list of essential Mac keyboard shortcuts. It turns selected text into italics. If it's already italicized, it turns italics off.
Use Control-Eject to bring up Restart/Sleep/Shutdown dialog on a Mac
Bring up the Mac's Restart/Sleep/Shutdown dialog box, as if you'd pressed the power button. Much more conenient to do it this way.
How to show the day, date, and time in your Mac’s menu bar
Check one little box and improve your Mac experience for every day moving forward. I wonder why Apple didn't set it up this way to begin with.
Get Mac System Information with a single click
Get detailed information about your Mac in a single move, under the Apple menu. What other people do in two moves you can do in one!
How to Type the Apple Logo
Every Mac users should know how to type the Apple logo. Turns out it's built into almost every font and it's easy as pie to do.
Print in a hurry on a Mac: ⌘-P, then Enter
Mac users: save a few seconds every time you go to print! The seconds you save add up. Maybe enough to learn to play the piano.