Is there a website that gives rules for suffix's? i.e. drop the "e" and add "ing"... I am trying to help my son finish a vocabulary list of words to combine with suffix's and don't remember all of the rules....

http://www.bbc.co.uk/skillswise/words/spelling/wordbuilding/suffixes/factsheet.shtml

This site is a good summary, and gives an exam if you wish.