CCNA  Cisco Certified Network Associate : Study Guide Written by Todd Lammle.  Published by Sybex Todd's book seems to be the standard for CCNA certification and with good reason.  The explanations are clear and concise.  You are walked through the commands and what they do.  A top notch preparation book for the CCNA exam.  You shouldn't rely solely on any book for this  exam though, you will want to add hands on router experience or experience on a router simulator to pass the exam.
		Managing I PNetworks with CISCO routers Written by Scott M. Ballew and Michael Loukides.  Published by O'Reilly Though first published in 1997 it is a very good refreshing course for those who do not have systematic education in TCP but still use it (and those who don't) in their work. Explanations are very clear, reading is easy and enjoyable. I believe the absence of details (what button to press and in what order) is its advantage.   300 pages versus usual 600+ is another definite advantage.
		Cisco CCNP Support Exam Certification Guide Written by Amir S. Ranjbar.    Published by CISCO Press This is the first book that I have read that was published by CISCO Press and I can't wait to read more.  This book comes real close to being the only thing you need to pass the 640-506 exam.  Amir throws in some real world experience and some good tips along the way.  A valuable addition to any tech library.