Emacs keystrokes supported by all OS X applications that use native text widgets.

Keystroke Description Mnemonic
ctrl-A Moves your insertion point to the beginning of the paragraph. A = beginning of the alphabet.
ctrl-E Deposits your insertion point at the end of the paragraph. E = End.
ctrl-D Forward delete. (Deletes the letter to the right of the insertion point.) D = Duh, you're an idiot
ctrl-K. Instantly deletes all text from the insertion point to the right end of the line. K = Kills the rest of the line.
ctrl-O Inserts a paragraph break, much like Return, but leaves the insertion point where it was, above the break. This is the ideal trick for breaking a paragraph in half when you've just thought of a better ending for the first part. O = Not Sure
ctrl-T Moves the insertion point one letter to the right--and along with it, drags whichever letter was to its left. T = Transpose letters.
option-delete Deletes the entire word to the left of the insertion point. When you're typing along in a hurry, and you discover that you've just made a typo, this is the keystroke you want. It's much faster to nuke the previous word and retype it than to fiddle around with the mouse and the insertion point just to fix one letter. N/A
ctrl-B, ctrl-F Moves the insertion point one character to the left or right, just like the left and right arrow keys. B = Back, F = Forward.
ctrl-N, ctrl-P Moves the insertion point one row down or up, like the down and up arrow keys. N = Next, P = Previous.

Other Useful Stuff

To set the tab width in most modes try:

M-x set-variable c-basic-offset N

Where N is the tab width in spaces.