Windows Clipboard keyboard shortcut

Open the Windows Clipboard by pressing Windows Key + V.

"To get to your clipboard history at any time, press Windows logo key  + V. From the clipboard history, you can paste and pin frequently used items by choosing an individual item from your clipboard menu. Pinning an item keeps it from being removed from the clipboard history to make room for new items."

The Top Mac Keyboard Shortcuts for Geeks

These are my top keyboard shortcuts for Mac, beyond just the normal copy/paste/etc.  I do a lot of freelance website development in Wordpress and also edit photographs in Photoshop.

Open Spotlight
Command + spacebar

Empty the trash
Shift + Command + Delete

New folder
Shift + Command + N

Switch between two windows of the same application (Firefox, Word, etc.)
Command + `    (same symbol as the tilde key)

Measure the pixels on screen or take a custom rectangular screenshot
Shift + Command + 4

Go back a field
Shift + Tab

Find again (Firefox, TextWrangler, etc.)
Command + g

Close Window
Command + w

Other favorites:

View Page Source code (Firefox)
Command + U

New tab (Firefox)
Command + T

New layer via copy (Photoshop)
Command + J