I'm planning to visit staples later this week and print out a poster sized gridded map for my D&D game. I haven't picked out a map yet though. Perhaps someone here can direct me to a good choice.

This is mostly an experiment to see if we will enjoy playing on a large, single image map rather than modular tiles. I would like a map that is versatile enough to be used numerous times in different scenarios. Maybe a dungeon with lots of rooms, a town with numerous small shops, a cavern system, etc. Can anyone recommend a specific map that will continue to be fun and useful for a while?

What resolution is good for printing at 24" x 36"?

Has anyone done this before and perhaps offer some tips or hints?