Open Maps?

Chilltowner asks: "I'm trying to get local (US) maps together for a community project. I want to able to modify and annotate the maps and provide them free to the public, creating a derivative open work. They also need to be accurate down to the street level and no more than 10 years out of date. I've been searching around for maps available in the public domain or under open licenses, like the Creative Commons licenses allowing derivative works. I've looked at the National Atlas, but the maps, though interesting, aren't detailed enough with street information. The topographical and aerial image maps available through that site are from Terraserver, which are copyrighted to Microsoft. Plus, I really just need simple vector road maps, not USGS rasters. I tried looking at the Census Bureau's TIGER line data, but I can't make heads or tails of it. Are there maps available through other agencies (national or international)? Are there Free/Open-Source Software projects that are making use of public data to build street-level maps for free (as in speech) use?"