I learned about HotPads from the Webware blog. It’s an excellent research tool for students, especially for English Language Learners. It’s primary purpose, though, is to advertise rentals and homes for sale.
It allows you identify cities on a map, and then lets you choose key demographic data — household income, average age, etc. Shaded neighborhoods then appear on the map along with a map key. You can also have the map show key points of interest, like schools.
The available information isn’t anywhere near as complete as what is available from ZIPskinny, another demographic data site I’ve posted about. However, HotPads is much more visual — by far.