Required Recommended
An Introduction to Modern Cosmology by Andrew Liddle
ISBN: 978-0470848357
Cosmological Physics by John Peacock
ISBN: 978-0521422703

Another text at roughly the level of Liddle's book is Barbara Ryden's Introduction to Cosmology (ISBN: 0-8053-8912-1). Also potentially useful, though out of print, is Eric Linder's First Principles of Cosmology (ISBN: 0-201-40395-1)

Last Modified: January 2010 subject to change