Start with something like the Google Maps building view like they have of downtown SF where you can see the outline of every building. Color the building based on what type of thing it is - restaurant, shopping, residential. That way you can just visually browse around a neighborhood and see - oh this street has the shopping, this area is really residential, etc.
Actually the maps that WalkScore makes are kind of decent, but they'd be so much better if the businesses were color coded and packed together by size instead of just icons plopped on top of each other. You know side of the street and you can estimate extents from the address range. The pop up icon tab things they use gives you a really false idea of what's going on in a neighborhood; it can look really rich with shops when it's not.
BTW that reminds me; I don't get why Google Maps isn't using the census data yet; that stuff is really cheap and would let you make really sweet population density maps.