Android has turn by turn, but if you like the peace of mind of having apps on your device without a Web connection and premium features like parking alerts, then take a look at a phone or tablet app like Navigon's MobileNavigator.
Navigon is currently discounting the cost of the Mobile Navigator app for Android - until May 30, it's selling for $39.95, down from $59.95. By contrast, the TomTom app for iPhone costs $89.99.
Key features include compatibilty with Android 3.0, with optimization for high resolution displays and a new "clever parking" feature which lets you take a close look at parking options before you get to where you're going.
Some of the other features could be accessed via other means - a weather feature lets you see weather information about your destination, and a destination information screen lets you look at eating and accommodation options. Tripadvisor and the Internet serve similar purposes, though ther is something to be said for the conveneicnes of doing all this from the one app.
One of the benefits of commercial GPS apps like this is turn by turn directions and auto-rerouting. Interestingly, Google has made this a free feature of its Google Maps Navigation app, though as Navigon points out in a press statement, its app provides "full function navigation" when a signal isn't available.
It's also worth keeping in mind that to get the "premium" features for Navigon's app, you'll have to pay extra. Red light camera and speed warnings (among other things), costs an extra $19.95, and traffic updates costs $29.95, while text to speech for street names costs $14.95.
If you're getting a Samsung Galaxy phone or Galaxy Tab 7in, you should already have the MobileNavigator app installed.