Fn: Function key
⇧: Shift key
⌘: Command key
^: Control key
⌥: Option key
⏏: Eject key
1. Fn+⌘+→ End of document
Going to the end of a document is very useful especially if it's a document that you constantly need to update or append. The simple combination of the function key with the command key as well as the right arrow will get you there. Substitute this with the left arrow and you are at the beginning of the document.
2. ⌥+⌘+⏏ Immediate sleep without dialog
Many Mac users tend to put their computers to sleep. You can do so very quickly by pushing the option, command, and eject keys. Some of the documentation says to push these buttons for 2 seconds, but in OS X you only have to push them once, shortly and you Mac will sleep.
3. ⌘+DEL Put item directly in trash
I'm not a fan of manually dragging stuff into the trash. That's why I like this shortcut, which promptly deletes items by putting them in the trash. The command and delete keys need to be pushed at the same time.
4. ⇧+⌥+⌘+DEL Empty trash without confirmation dialog
Do you want to really delete something, without having to go through the dialog boxes? Then if you push these buttons together, shift, option, command, and delete, your trash will be emptied without a confirmation dialog. Once these buttons are pushed, there's no going back.
5. ⌘+ arrows Navigating a document, ⌘+⇧+arrows Selecting portions of a document quickly
I usually go through documents fairly quickly using the keyboard shortcuts. You can experiment with these. Adding the option key, ⌥, will take you to the next word in a sentence. Adding the shift key, ⇧, will select text as you navigate through it. It's very quick when you are editing text files.