Check out SFGIS – San Francisco Enterprise GIS. A very interesting site for those living in the city of San Francisco, or thinking of moving there, but also of interest perhaps to people in other cities as a sign of what might be coming (many cities are now using this technology, but just not making it available online).

In particular, look up an address using the SFParcel tool, then when the detailed map appears click the Photos button over the map to add the overhead photo underlay to the map. Very, very cool. For those outside of SF who want some addresses to start with try:

• 1 California Street
• 600 Montgomery Steet (the Transamerica Tower)
• Block 9900 Lot 039 (Pier 39)
• 1047 Lombard Street (the crooked street)
• 280 Telegraph Hill Blvd (Coit Tower)

New York residents should take a look at their city’s system: New York State GIS Clearinghouse. I could not find the same easy access to maps there based on street address, but the Raster Imagery is pretty impressive if you know where you want to look.