I would definitely recommend getting the 4th edition of the Parsley (formerly Overton) book. It was updated and a lot of things were added. But a used copy of the 4th edition would work just as well as a new copy
T$, you're two main choices are Overton/Parsley or Edgar Souder's Bust Half Fever. These are the standard references. I don't have Souder's book, I hear its excellent. I do have the Overton guide, of course.
If you don't want to drop the cash on a book (they aren't cheap), I also reference coinzip quite a bit:
http://coinzip.proboards.com/index.cgi?board=lebust
I definitely use the book as a reference, but I also pull it out and just look through it to relax sometimes. I'm always learning what sort of things are good identifiers, what to look for on certain varieties, etc. I don't really memorize individual varieities, more like getting familiar with everything.
