There are many ways to add a map to a web page. Here is one more from ESRI. It's called Mapping For Everyone and it is in Beta. This is U.S. only.
What you see above is a choropleth map of the City of Poughkeepsie (New York) by unemployment rate, a rather hot topic! This is tract-level data. The data source is "estimated July 1, 2009 unemployment rate in the United States." There are currently only seven different demographic variables to map, but since this is in beta and since people love to map demographics of all sorts, my guess is that ESRI will add more data.
Here's what you do:
1) Enter a zip code, then 2) choose a demographic variable from the drop-down list, 3) size your map to the dimensions of your web page (for instance, the map above is 500 pixels wide), then 4) share your map, either as a link, or as html code to embed into your web page.
Thanks for the tweet, Joseph Kerski!