Control + Option + Command + Eject shutdown time image This option is used to shutdown your Mac. This nice thing about doing this instead of shutdown menu is it bypasses the counter and immediately starts shutting down.
Command + Option + Eject Puts the computer to sleep bypassing the countdown.
Control + Shift + Eject Allows you to put the display to sleep
Command + Space-bar shutdown time image Use this shortcut to open up the spotlight bar to search for an application or a file.
Command + Shift 4 This will allow you to select an area of the screen to take a screen shot of. Generally your picture will be dropped to your desktop.
Control + Command + D Dictionary shortcut. This is not my most used command but it can be useful in situations
Command + TAB If you are familiar with Windows this is kind of like the Alt+Tab functionality to switch between open applications
Option + Command + M Sometimes you just want to minimize everything on the screen to remove some clutter.
Command + , Open up the preferences window for your application
Command + ← / → / ↑ / ↓ These commands are useful when handling a document or text.
Command + ← or → will take you to the beginning or end of line.
Command ↑ or ↓ will take you to beginning or end of page.