Navigate Finder Folders Quickly.
These keyboard shortcuts are used to navigate around the Finder, they can also be used when in a save dialog to navigate to these folders.
On an open Finder window;
Command + Shift + A - Open the Application Folder.
Command + Shift + U - Open the Utilities Folder.
Command + Shift + D - Open the Desktop Folder.
Command + Option + L - Open the Download Folder
Activate screen corners.
Activating screen hot corners is a great way to save time instead of using a keyboard shortcut or even navigating menus, you can just mouse over to a corner and the selected task will be performed.
Go to System Preferences > Mission Control > Hot Corners. Then choose what corner you would like to set a shortcut on.
Show the date on the menubar.
Probably obvious to some, instead of having to mouse up to your menubar and then click on the clock to see the date, enable it in System Preferences > Date & Time > Time so you can just quickly glance up to see the date.
Quickly Shut Down Your Mac.
Control + Option + Command + Eject - shuts down your Mac.
This is a great time saver because it bypasses the 60 second timer you get when using Apple menu & Shut Down or Control + Eject.
You can also use Option + Command + Eject to make you mac sleep.
More Useful Keyboard Shortcuts.
Shift + Command + I - In Safari and possibly other Apple Apps, will automatically generate a new email and paste the link of the web page you were browsing in the message.
Highlight text then - Shift + Command + Y - Create a sticky out of the highlighted text, works in Safari and possibly other Apple Apps.
Control + D - Delete files/folders
Control + Option + Command + 8 - Invert Screen Colours, useful for night-time reading.
Highlight a word then - Control + Command + D - Define that word.
Command + Shift + 4 + Space bar - ScreenGrab current window.
Option + Command + M - Minimize ALL windows.
Option + Shift + Command + Esc - Force quit currently focused app.
Command + up or down arrow key - Scroll to the top or bottom of a webpage.