HealthyChildren.org
From the American Academy of Pediatrics. 

Pediatric Advisor
Excellent information on many newborn issues.

KidsHealth.org
All sorts of information about pregnancy and newborns.

The American Academy of Pediatrics
Topics can be searched by typing in the topic or by scrolling through a list of topics.  Topics can also also listed relative to the age of the child.

March of Dimes
Pregnancy and newborn information.