Android phones, apps and tablets

google maps!! fully updated, show's current traffic/shortest route and iz free.

I've used the TomTom app. Not the cheapest but has all the functionality of a full sat-nav with the bonus of all maps being available offline (useful for travelling/crap reception).

Google Maps navigation is scarily good.

So good I don't even use a mount or screen. I just connect the bluetooth to the stereo in my car, put some music on, and let Google Maps reduce the volume to give me spoken directions.

And it hasn't failed me once.

Seriously, not a missed turning or anything.

And without having the screen on, I barely use a couple of % of battery in a 1 hour drive.

I can't recommend Google Maps highly enough for sat nav.