I hope my comments aren't considered biased, due to being a sponsor and owning Herp Books. I was a reptile book fanatic long before I owned the book store.
It all depends on what you're interests are. For captive husbandry/breeding, of course you can't go past Keeping and Breeding Australian Pythons and Keeping and Breeding Australian Lizards by Mike Swan. They contain lots of very useful information, but they are designed to be affordable reference guides, rather than impressive collector's items such as Dave and Tracey Barker's "Pythons of the World, Volume One: Australia". Although it's out of print, it comes up for sale a few times a year and is worth the price just for the amazing photographs, many of which are of rare localities/specimens.
The number one book that anybody with even the slightest interest in reptiles should read is Rick Shine's Australian Snakes - A Natural History. This book will make everything make sense...it's due for an update but it's still a very modern book.
If you're looking for a field guide, the only one to go for is A Complete Guide to Reptiles of Australia by Swan and Wilson. It's regularly updated, contains every species officially recorded in Australia and is easy to use. There are several state and "area" based field guides too, but they aren't necessarily considered a bible. The latest edition Cogger is now 11 years old and is quickly losing it's place as a relevant reference book.
There is a ton of readily available, out-of-print Australian books out there that are desired though - Ehmann, Wilson and Knowles etc, but they haven't reached the "must have, bible" status of the others I mentioned above.
