Have you all played around with Zipskinny? It’s a site that takes data from the 2000 census and lets you search by ZIP code to see demographic information in your area, and compare it to others: income levels, racial breakdown, unemployment, education level, marital status, etc. It’s pretty basic information, little more than a snapshot, but it’s a good snapshot and a really nice interface.
I would think it’s pretty easy to do a good mashup with crime statistics, using the data from sources like this excellent NYPD site — although ZIP codes and precinct boundaries aren’t the same. The NYPD precincts each generate a weekly crime report, like this one from my neighborhood.
(Hat tip: Matt Wecksell)