I've found that a lot of it depends upon your background, in general. People that started in the old DOS days often have an easier learning curve. If you can get into a large bookstore and 'prowl' the computer section, you'll see 'in a hurry' what you find most easily readible. Just watch the versions of the Linux covered, as there are a lot of old versions out there. I liked Learning Red Hat Linux, by Bill Mc Carty (an O'Reilly Book), but it is getting dated as version 2 is based upon RH 7.2
http://www.oreilly.com/catalog/redhat2/
Red Hat Linux 8 Bible, by Christopher Negus, has a lot of material directly related roughly 35, if you buy it right or 49.99 list.
Red Hat Linux 8 for dummies, should be pretty good, if it followes the style of Most of Jon Hall's books.
Red Hat has a lot of books written about it