The Extravagant Universe: Exploding Stars, Dark Energy, and the
Accelerating Cosmos, R. P. Kirshner (Princeton University Press,
Princeton, 2002).
A good online source of cosmological information is:
Ned Wright's Cosmology Tutorial,
http://www.astro.ucla.edu/~wright/cosmolog.htm
The following cosmology textbooks are arranged in increasing order of technical difficulty:
Cosmology: The Science of the Universe, 2nd ed., E. Harrison
(Cambridge University Press, Cambridge, 2000).
Cosmology: a First Course, M. Lachièze-Rey (Cambridge
University Press, Cambridge, 1995).
Principles of Physical Cosmology, P. J. E. Peebles (Princeton
University Press, Princeton, 1993).
The Early Universe, E. W. Kolb and M. S. Turner (Addison-Wesley,
New York, 1990).
The Large-Scale Structure of Spacetime,
S. W. Hawking and G. F. R. Ellis (Cambridge University Press,
Cambridge, 1975).