My favorite so far is the Pratical Guide to Red Hat Linux 8, by Mark Sobell. 'Excellent' is all I can say about this book. Excellent regardless of your current distro, even. Do not confuse this with the current version of the book, Practical Guide to Fedora Core, as it is about 500 pages shorter and lacking in all the details that made the previous version so great.
In fairness however, Sobell has a book coming out soon on shell programing, and I think what has happened is the one big book was split into two smaller books, but for now the RH8 version is still the best single book IMHO.