Go to the home page and scroll down to clubs. You will find... Variety Nickels A place to discuss nickels.
I have been having a hard time finding die marker information and images. What I've been doing is visiting http://www.conecaonline.org/variety_listings.html for their Jefferson varieties then search the DDO/DDR/RPM number on ebay for images. If nothing is found even in completed listings then I hunt google for dealers who have images. Tend to save them all to the hard drive for easy IDing. There are a few books that cover errors and varieties but they are so hard to find or over priced its crazy. Good luck.
At this time the CONECA files are the best site when looking for the Die Markers for varieties. VN is still under work.... There are some great books out there if you are interested in nickel varieties. The books by James Wiles, and Nagengast are the best IMHO. Check on ebay---the books by Wiles are out of print (at least Vol 1.) and Bernard Nagengast sells his books on ebay all the time. Speedy