The history of the Universe: decoupling of the relic radiation and synthesis of the light elements
Note: Prerequisite Knowledge:
A good background in basic undergraduate physics would be adequate.
Some excellent popular-level books are:
1) The First Three Minutes (2nd ed 1981) - Steven Weinberg
2) Darkness at Night: A Riddle of the Universe (1987) Edward Harrison
3) The Poetry of the Universe: A Mathematical Exploration of the Cosmos (1995) - Robert Osserman
4) The Little Book of the Big Bang: A Cosmic Primer(1998) - Craig Hogan
5) Quintessence: the Mystery of Missing Mass in the Universe (2000) - Lawrence Krauss
Recommended undergraduate texts are:
1) Introduction to Cosmology (1995) - Jeremy Bernstein
2) Introduction to Cosmology (2nd ed 1997) - Matt Roos
3) An Introduction to Modern Cosmology (2nd ed 2003) - Andrew Liddle
4) Introduction to Cosmology (2003) - Barbara Ryden