I really have only two: the Camel and Perl Pocket Reference. I also have CGI Programming wtih Perl (Guelich, Gundavaram and Birznieks) but I don't find it very useful and seldom refer to it. Actually, most of my Perl reading (apart, of course, from Newest Nodes) has been on CPAN - I find reading module docs, and looking through the functions, a top hole way of learning good programming in general, as well as learning to use the modules in particular.

§ George Sherston