The idea of "Linux for Dummies" seems a little strange at first (should dummies be using Linux in the first place?). But the book itself (written by Jon "maddog" Hall), is an invaluable resource for people who want to learn Linux (and Unix), commands without having to decipher instructions like "Usage: rm (-fvrist) (W!) (-) (--) name ...".
The book walks the user through many basic functions, like installation and configuration of X, using vi, and many other common applications. The book is a little biased towards the RedHat distribution (it even comes with a RedHat CDROM), but it can be useful no matter what distro you are using.
This book has been invaluable to me on several occasions (like in reinstalling lilo, and figuring out how to create user accounts from the command line).
You can purchase this book for $24.99 from IDG Books (although it can be had much cheaper on eBay).