Well I took the plunge, and am now Linux+ / LPIC-1 certified!
I have been playing with Linux for nearly 10 years, so a some of it wasn't new, but this was an invaluable learning experience!

I used the CompTIA (powered by LPI) Linux+ Complete study guide by Sybex.
It's a great book, however watch out, there are a couple of typos in there (there was a command or two that had double quotes, where single quotes were required), but if you try out all the commands, you will pick up on them.