For road navigation I found something called Sygic, I have been trying it on my phone while driving. Once I got the lady with the British accent to tell me miles & yards instead of meters & kilometers it is fairly good. You can download maps for off line use, and if you have a data connection it will tell you about accidents, traffic, speed cameras, etc. For tablet use I would have to link my phone to the tablet for the data connection to work.
Do most of the tablets these days have GPS built in? I have a older USB GPS but internal would be more convenient.