Lots of tips on the General/CommandLineInterface at:

http://www.osxfaq.com/tips/unix-tricks/

OS X Hints: http://www.macosxhints.com/ has quite a bit of information also.

Unix Tutorials

• (Beginners) http://www.ee.surrey.ac.uk/Teaching/Unix/
• (Advanced) http://www.uwsg.iu.edu/UAU/uau.html