Lexicons are specialized dictionaries that contain the meaning of words alongside significant variations that occur within a particular group of texts (in this case, the New Testament).
A Greek-English Lexicon of the New Testament and Other Early Christian Literature by 
Greek-English Lexicon of the New Testament by 
A Concise Greek-English Dictionary of the New Testament by The Theological Dictionary of the New Testament is a comprehensive dictionary resource. The 1st volume of the set is an abridged version of the dictionary organized by English transliteration. The final volume of the set, vol. 10, contains an extremely helpful index -- a scripture reference index and index with English translations -- with directions to the larger dictionary entries in other volumes.
Theological Dictionary of the New Testament by 