It is difficult to find maps and guides with just Delaware as the subject. They are almost always bundles of several states. The ones that we find most useful are the Frommers guide and the Rand Mcnally maps. We also pick up local brochures at the welcome centers and in the motel lobbies to fill in any missing pieces of info about the area we are visiting. So stuff a Frommers and Rand Mcnally in your pack to start with. The Frommers is actually pretty decent reading on the trip (just don't do it while you are the designated driver).