I had given trapster a try earlier, but never really liked it. There was also another similar app that was even worse. Now I'm using Waze
and loving it. The biggest difference is that waze is a full on crowd sourced navigation app with the ability to report road hazards, traffic, and speed traps.
Crowd sourced because the whole map is generated by people driving around. It started out in Israel where a couple hundred thousand users completely mapped out the entire countries roads just by doing their daily driving. However, the US version started with the census bureau's free maps as a base.
As you drive around your car become pacman and you gobble up dots on unconfirmed roads. Adding new roads is pretty easy. The online editing map is pretty cool. I just drove through a new neighbor hood near my house, and then went online and added the roads on top of the route I drove. After about a week it showed up on my phone and I drove over it again to eat the "cookie points" and confirmed the road was there.
The navigation part is still pretty weak, but it learns fast. I wouldn't rely on it to get me somewhere I'd never been, but the developers even say it's meant to assist you in driving a route you regularly drive such as your commute to work. It's really good at showing heavy traffic, and alerting you to it. When I've gotten stuck, it automatically notices I'm going slower than the speed limit and updates the map. It's a shame that more people aren't using it.
Oh, and it's FREE, for iphone, android, and windows phones.