Here are the books on my bookshelf that have helped me along the way in my studies. Hopefully you will find them useful as well, in no particular order.

Cisco Press

Cisco LAN Switching Fundamentals
Author: David Barnes, Basir Sakandar
ISBN: 9781587058493

CCNP SWITCH 642-813 Official Certification Guide
Author: David Hucaby
ISBN: 9781587202438

CCNP ROUTE 642-902 Official Certification Guide
Author: Wendell Odom
ISBN: 9781587202537

CCNP TSHOOT 642-832 Official Certification Guide
Author:Kevin Wallace
ISBN: 9781587058448

Implementing Cisco IOS Network Security
Author: Catherine Paquet
ISBN: 9781587058158

CCNA ICND2 Official Exam Certification Guide
Author: Wendell Odom
ISBN: 9781587201813

CCNA ICND1 Official Exam Certification Guide
Author: Wendell Odom
ISBN: 9781587201820

CCNA INTRO Exam Certification Guide
Author: Wendell Odom
ISBN: 9781587200946

IPv6 Security
Author: Scott Hogg, Eric Vyncke
ISBN: 9781587055942

Voice over IP Fundamentals
Author: Jonathan Davidson, James Peters
ISBN: 9781578701681

Securing Your Business with Cisco ASA and PIX Firewalls
Author: Greg Abelar
ISBN: 9781587052149

Cisco ASA and PIX Firewall Handbook
Author: David Hucaby
ISBN: 9781587051586