Can you list any of these apps?
Along with MotionX mentioned above, Navigon and TomTom will also work fine. The easy way to figure out if an app will work without a data signal is to look at the size of the app download. If it's huge it includes maps. Navigon and TomTom are around 900MB.
MotionX lets you download map segments to the iPad for regular road, topographic or marine navigational.