At work on Saturday and catching up on my RSS feeds. DataPlace is an interesting site mentioned by the LibrarianInBlack.
It gives you the ability to quickly search for data on a city, place, or zip code. This is stuff you can also get from the census bureau but what makes it really interesting is the ability to compare places. Here is a link that compares the zipcodes of two places where I have worked.
I sometimes have a person call who wants demographic information about different places and this site will be very helpful. This is going in delicous for sure!