I don't have a large collection, but I use a few tools that have come in handy whilst exploring old roads.
My oldest is a 1926 Automobile Blue Book, Vol. 2 (Southeast and Mid Atlantic). The road descriptions were still there, but whenever the route followed a state highway, the turn-by-turn directions stopped. Luckily (for me, anyway), Mississippi didn't implement a state highway system until 1931.
My second oldest item is a 1932 Rand McNally map of Mississippi. It's helpful since the ABB map shows almost no roads other than ABB routes. It also shows the subtle (some not so subtle) changes in the state highway system. Also handy are the ten or so city maps.
My most practical for roadtrips (thus, the one I never leave at home) is a 1957 Rand McNally 48 state, Canada and Mexico atlas. There are some four lane and expressway segments shown, but there isn't an Interstate shield to be found.
I have several newer atlases (next-oldest is 1981), but until I'm out of college, I don't have much to spend on collecting maps/travel guides. I spend enough on gasoline as it is <grin>.
CityBoy1986