Cool vi(m) commands

:u Undo.  (File under "Duh," but this really is the best.)
:e ~/ Explore; in this case, the home directory
:bro ol Or more verbosely, ':browse old'.  Hit 'q' then type appropriate # to edit that file.
:sh execute shell command.  exit will return to vi.
Ctrl+W, S (upper case) for horizontal splitting
Ctrl+W, v (lower case) for vertical splitting
Ctrl+W, Q to close one
Ctrl+W, Ctrl+W to switch between windows