Alacrity

Google Maps the census: "This Google Maps mashup from AnalGIS and SRC adds census information from the 2000 census to the Google Maps interface we already know and love.
Just put in your address and you can quickly see the population, income, and housing statistics for your area in a 1, 3, and 5 mile radius of your home. "

What's really crazy is to pick a big city and see the demographics change as you pick suburbs. My grandparents live in Mountainbrook, AL: average income within 5miles= 107k. Just one click over in downtown B'ham: average income= 28k.