DeLorme Gazetter maps are the best all round maps I have found for trip planning. They cost about $20 so planning a cross country trip with these could get expensive. You can find these at WalMart if you want to check one out.
They have lots more detail than your typical maps not enough in my opinion. Road names are pratically no existent this can be a problem when you are trying to find your turn unfamiliar territory.
They show back roads they don't indicate if the road is paved or not. To be fair neither do other maps with the one notable exception being DOT county maps.
DeLorme Gazetteers are also available as topographic maps. I have never seen one of these.
I use a combination of these and Google Maps to plan trips.