xoom
I know its expensive, and I would assume the new Asus or Acer tablets also have a GPS, but with the xoom you get a 3g radio so you can use Google's navigator. It works really well.. the other tablets, you would need a off line GPS maps.
Navigon sells an android app with off line maps.. I would assume it is exactly like their GPS units they sold a few years back.. my mom has a Navigon, and she loves it. but Navigon sells its app only in Europe .. the app was about $40 and I would be happy to buy it, except its not offered in the U.S.
I would recommend a 3g Xoom. As longs as you can get connected to a 3g service, your good.
Verizon usually has really good coverage... but you can't use googles navigation unless your connected.