I'm using a Samsung Galaxy Tab - the 5" model. it slots right about into the space formerly occupied by my AM radio in my Electravan.
I generally like it and have been pretty happy. I think i paid about $150. It has a dedicated GPS in it and plays well with google maps.
My BMS (elektromotus) has an android app that picks up it's bluetooth signal. should be a pretty sweet little setup, but I'm still working on my lithium upgrade so you'll have to ask me in a couple of months how it all works.
You can pick up the old Dell streak 7" for under $100 these days, similar specs and actually I hear the GPS in it is quite good & sensitive.
http://dealnews.com/Refurb-Dell-Streak-7-16-GB-Android-Tablet-for-100-after-rebate-free-shipping/634404.html
The one thing I might try to get if I were doing it again is one with 3G access in addition to wifi, which would allow me web access without first having to tether it to my phone. but also would cost another $10 a month or whatever. meh.