I don' t know about the best sites on the net, but I can give ya a few sites I use to get topos off of. Try some of these and see what ya think of em....

http://www.maptech.com

http://www.topozone.com

http://terraserver.microsoft.com/

you could also go to your local DNR website and see if you can order State Forest maps free, and have them delivered to your door. I know my state DNR site allows you to do this!!

Outlaw