There are electronic word banks like
http://www.jbox.com/PRODUCT/GW9600
or
http://www.goodsfromjapan.com/produc...20Dictionaries
might be useful, though expensive. I don't know if they teach usage rules. The Casio model has an input area for writing kana, which is pretty cool. Looking at the specs for the Canon, it has something like 500000+ entries, though many will be duplicates.