look for crow bars, coil springs, leaf springs, old chisels and punches, lawnmower blades, old files, saw blades, all of those are great carbon steels, but you may want to do a spark test on some of them just in case. also look for any usable round stock square, flat, etc. I always come back from the scrap yard with something I wouldn't expect to find there, so just keep your eyes open. this will be a very fun and rewarding hobby.
Littleblacksmith