This book is by far my favorite. Peter Gurney really knows his guinea pig information!

Proper Care of Guinea Pigs (Proper Care Of... Series)
by Peter Gurney

The Guinea Pig Handbook
by Sharon Vanderlip

A Grown-up's Guide to Guinea Pigs
by Dale Sigler

Guinea Pigs : A Complete Pet Owner's Manual (Barron's Complete Pet Owner's Manuals Series)
by Katrin Behrend

The Guinea Pig : An Owner's Guide to a Happy Healthy Pet (Owner's Guide to a Happy, Healthy Pet)
by Audrey Pavia

The Essential Guinea Pig (The Essential Guides)
by Betsy Sikora Siino (Editor)