Alameda as seen in OpenStreetMap on 2011/04/21

OpenStreetMap is a work-in-progress mapping website / interface that aims to produce an entirely free (as in speech) set of maps of the world - thus they can be used on our wiki without having insurmountable copyright issues that might be the case with other sources. The maps are contributed by regular people. Unlike things like Google Maps, OpenStreetMaps are freely usable by anyone for any purpose. All the software that powers the site is freely licensed as well. For these reasons, it has been considered a potential option for wiki mapping at some point in the future (read more here if you're interested).

The Alameda map data seems to be pretty good - an import of some national data information and lots of people working to tidy it up has made it pretty complete. There is a bunch of need to join up road segments and add new data such as names and amenities like drinking fountains and postal boxes. Is your neighbourhood accurate? If not, you should fix it. There is also an Alameda County page on the OpenStreetMap wiki which might detail any group efforts in the region.