Abbreviations: Hbk = Hardback, or hardcover.
Pbk = Paperback.

Discovering Sharks edited by Samuel Gruber. Retail: $10.85. Amazon: $10.85. Pbk.
This is wonderful little book filled with great papers by a number of shark researchers. The papers cover all topics dealing with sharks, from classification to reproduction, and behaviour to conservation. It provides a nice, concise, overview of shark biology and behaviour, and research done to date on the topics. Very recommended.

The Reproduction and Development of Sharks, Skates, Rays and Ratfishes edited by Demski and Wourms. Retail: $169.50. Amazon price: $169.50. Hbk.
Just in case you're into shark reproduction and have $170 to spend, this is the volume for you! This is pretty technical, but it is the most in-depth and up to date treatment available.