The January edition of Pediatrics summarizes much interesting information about US demographics in 2007:
Births: 4.3 million
Deaths: 2.4 million
with a life expectancy at birth of 77.9 years.
The birth rate (per woman 15-44) is actually rising currently at 66.9 births/1000 and this is above the population replacement rate, meaning we don't seem to be facing the demographic time bomb to the same extent as Japan and much of Western Europe. I figure these kids will start paying social security taxes about when I retire.
An old post details how badly Allergy fellowship applicants fare when asked to estimate the number of births in the US each year.