Open or Low Cost Map Data

Zugla writes: "With google and yahoo's online maps becoming more powerful and easier to use and gps units with built in maps becoming the norm, users are beginning to expect maps and map data in all sorts of applications. I produce automatic market reports which are distributed via email in pdf form and I would like to include annotated maps showing comparable locations and other data. Because including these maps in a distributed (not free) report would be a form of republication, I do not believe I can use google (terms of service) or yahoo's (terms of service) offerings. Are there other sources of free or low cost map or map data?"