I just found this site http://babynamewizard.com which shows a graph of nearly 5,000 names and their usage percentages over the course of more than 100 years.  It's incredible!  You just start typing in “J” and it shows all names that start with J and you can see the trends of baby names like “John” and “Joshua” and others.

One of the most interesting capabilities of this tool is that you can see names that die-out and names that come into use that have never been used before.  It's a very interesting tool even if you're not expecting (my wife and I are expecting a boy in August of this year :-)