My colleague in communications, Jason Brittain, has finished revising Tomcat: The Definitive Guide. The Second Edition was just released (October/November, 2007) and covers Tomcat 6.0.  Coverage has been expanded in almost all areas; the first edition's 295 pages are dwarfed by the second's 462 pages.  If you're using Tomcat, this is the book you should have to help you along!