http://www.t206.org/value.php
I like this tool since it accounts for back variations and grades. Of course its not 100% accurate but it gives people a rough idea of what a card might be worth. Some times I find it well short of reality, and recently I have found it over valuing some things I like.
The links on the left also lead to
http://www.t206museum.com/page/backs.html which is a good discussion of backs. The blank back is not as scarce as the Piedmont 42 but is more scarce then the Broad Leaf 350....and oddly enough I bought a P42 for 1/2 what I paid for a BL350. Go figure...
