Open Street Map - wiki-based user created street maps
Have you ever wondered why smartphones like Blackberries and iPhones don't provide turn-by-turn directions in their Google Maps programs? The answer is probably not what you think. It turns out that the map imagery that is used in Google Maps has licensing restrictions against it, preventing it from being used for turn-by-turn directions. Although it's easy to find various mapping sites online that provide free access to geographical information, it's very hard to find actual maps that can be used in applications that aren't extremely expensive or who's use is heavily constrained by license restrictions.
Open Street Map is a project that was started to create a completely free set of maps that could be used by anyone in any creative way they can imagine. The site operates like a wiki, where users are encouraged to contribute information when they can. If you've never been involved in making maps before, that's okay; the site includes a beginner's guide and a very comprehensive map making reference.
While the site isn't as slick as Google Maps, there's something satisfying knowing that the maps are unencumbered by heavy license restrictions. If you like it, you can use it in your own application - how you want. A quick comparison between Open Street Map and Google Maps looking at my neighborhood showed some apparent differences of scale, though either would work well for driving directions. Interestingly, Open Street Map is more up-to-date in my area, including a road that was only completed a few weeks ago as part of a new shopping centre.