DataPlace lets you plot one or more demographic factors in a Google Maps interface, and create an embeddable web page widget:
Data includes social/ethnic/economic/population/health/etc., and can be plotted at any detail level from census tract all the way up to national; plot multiple parameters on one map, or display two maps side by side with different parameters. Charts, rankings and metrics, too, all embeddable on any website in widget form (like above).
Be warned, though – site is labeled as “Beta” for good reason. Even with a decent help section, figuring out how to do anything is a real chore. And if you’re impatient, avoid this site – it can take several seconds for data selections or map/chart displays to refresh. Very much a work in progress, but there’s good stuff if you’re willing to slog through the difficulties.