If you are considering some off-road riding (or even if you're not), I like the United States Forest Service maps. As of their date of publication, they indicate whether roads in national forests are paved or not. Since most of them were published within the past twenty years and we haven't been converting many unpaved roads to pavement in that time, I have found them to be pretty accurate in that regard.

USDA Forest Service - Caring for the land and serving people.