Other
Purdue University: Virtual Library Developmental Biology
A good resource for background into the entire scope of biological development. A list of terms will yield more depth on your choice.
Earth Life
Earth Life: The Placental Mammal and Reproduction
A very good site which covers the basics of mammal reproduction, in particular, placental mammals.
CK-12 Foundation
Ck 12: Life Science: Mammal Reproduction
[Free Registration/Login may be required to access all resource tools.] Mammals don't typically lay eggs, but monotremes are the exception. All other mammals give birth to live young and belong to one of two categories, the marsupials...
Earth Life
Earth Life: The Wonder of Milk
An interesting article on the production and value of mammalian milk. This is good insight into some of the critical factors affecting mammalian development.