Learn the Command Line the Hard Way -
a somewhat long, but complete (exercise-heavy) guide to using the command line.
If you're not already comfortable with the command line, you should do this.
If you're comfortable with the command line, you should still probably do this.
OS X's Terminal application has a lot of configurable settings under
Dotfiles can help make your
command prompt beautiful.
Learn to Program (Chris Pine) -
Great into to programming in general, that uses the Ruby Language. Suitable for beginners, intermediates may get something out of it as well. It's very thorough and clear, building from the bottom up.
HCI Class - excellent online course. It's definitely
worth watching the first couple (3?) of weeks' lectures at least. (You can watch
lectures if you click "preview course" even if you don't sign up [although
it's free and riskless to sign up and keep track of your progress].)
UX Crash Course -
a good online resource which goes through design fundamentals