From a friend - I just found out about this myself.

Ohio Byways:
http://www.ohiobyways.com/

When you go to the ohiobyways site, move the rectangle around on the Ohio state map to see routes on different parts of the state. There's a buncha stuff there....

Byways:
http://www.byways.org/

This one has byways across the USA, organized by state. You choose a state on the menu on the RH side of the page, and get a map marked with the various byways in that state. Click on the byway, and you get detailed info on selected route and its history.