Good resource for learning UNIX command-line

When I upgraded from OS 9 to OS X years ago, I was a little iffy about Terminal and using UNIX command-line. It sure felt like a step backwards because being a person that was using computers since the Mac Plus, the GUI was supposed to be a step-up from command-line. Luckily, there hasn't been many times I had to rely on the Terminal to get things done.

However, I'm becoming more and more interested in learning (and I have the time to learn). So what's a good book and/or webpage to learn UNIX command-line for newbies and work my way up?