The Breen encyclopedia on
Half Cents is excellent, next one you should try to find is Manley's
Half Cent Die States!
"A Quickfinder for Attributing Varieties of Business Strike United States
Half Cents 1793-1857" By Gregory S. Heim is out now in the 2nd edition, and is a great help to attributing those varieties I've found, not too expensive either - I got mine directly from him on
ebay.
"Buy the Book Before You Buy the Coin" - Aaron R. Feldman - "And read it" - Me 2013!
ANA Life Member #3288 in good standing since 1981, ANS, Early American Coppers Member (EAC), Colonial Coin Collectors Club member (C4), Conder Token Collector Club member (CTCC), Civil War Token Society (CWTS) member, Liberty Seated Collectors Club (LSCC) & Numismatic Bibliomania Society member (NBS), USMex, Member in good standing, 2¢ variety collector.
See my want page:
http://goccf.com/t/140440