Strong's Exhaustive Concordance by James H. Strong lists every occurance of all but 47 words (like "a", "the", etc.) in the King James translation of the Bible, along with a number indicating which original word it was translated from. This allows you to gather more of a feeling for the meaning of a word by observing other contexts in which it was used. This number can also be used to look up a definition of the original word and find other ways it is translated.