The Sport Americana guides to non-sports cards provide useful for information on many of the non-sport cards out there. I believe that there are 5 of them covering different eras.They are a must for any non-sport card collector. The price guides in those books are outdated,however, as most of them are decades old
For a more accurate price guide, check out the non sport card update which comes out every couple of months. It has a price guide in every issue although it's not the best reference for some obscure company issued sets.
The SMR report issued by PSA every two months also has a non-sport section. Although the mags are only available to PSA members, some copies are available on e-bay and worth checking out.