Maps, particularly post-apocalyptic and pre-civilization maps. This one is specifically relevant to me as I'm researching/collecting resources for a book set in Post-Roman Lothian and the surrounding Scottish lowlands. I've been digging around for quite a while and I haven't found a high-resolution geographic and political map of the British Islands from around 450 AD.
In addition, I used to play the hell out of Rifts back in the day, loved the Rifts England setting, and am currently running Shadowrun game that relies heavily on ley lines. So... yeah, this map is smack in the center of a Venn Diagram of several of my interests.
Also, not sure if you're part of the Cartographer's Guild, but I think that community would seriously dig your work. cartographersguild.com/