Linux Command
One resource I've found really helpfully in learning Linux is the web site www.linuxcommand.org. I don't know who made it or why but it *REALLY* helped me understand the fundamentals of writing Linux shell scripts (which can be amazingly helpful in many situations) and in just understanding the linux command-line interface better. (A shell script is kind of like a DOS batch file - only more powerful IMHO)
They really did a good job with this site and I would encourage anyone who's new to linux to check it out.