Although, i don't have the habit of reading books, here are a few books which you may consider reading.
Database Hackers Handbook.(David Litchfield)
Oracle Hacker's handbook (David Litchfield)
Hacking Web Applications Exposed (TMH Publications)
Essential PHP Security (Chris Shifflett)
TCP/IP Illustrated (Comer).
Hacking Linux Exposed.
As this list is really small, it is clear that i need to read more books. If you know any good book related to pentesting (or security in general) please share it with us.