eReaderMaps has an even dozen of their map titles free in the Kindle store. These titles are specifically designed to be used on a Kindle device (although they are optimized for larger screens).
The only catch?
The free maps are all for cities in Australia and New Zealand (and half of them are in German). Still, looks like they may be interesting for those planning on visiting either country or those who live there, that haven't memorized every street in a particular city. I'd think they would also be quite useful for any author who is planning on setting one of their works in one of the cities covered.