Useful stuff from /.

In bash

!! runs last command.
!vi runs last command that began with 'vi'.
!?vi runs last command that had 'vi' somewhere in it.
!!* expands to all arguments of last command.

And here is the unix alarm clock (for an 8hr nap)
sleep 8h; cat /dev/urandom > /dev/dsp

Enjoy!!
(additions are welcome).