Koine Greek Reader and Septuagint Vocabulary Lists
Prof. Rodney Decker is the creator of Koine Greek Reader, one of my favorite resources for learning and practicing Greek. The book includes grammar review, vocabulary lists, and Greek readings with helps. The Reader covers the New Testament, the Septuagint, the Apostolic Fathers, and a few early church creeds (which are really fun to look at in Greek).
His resources page has some very helpful Septuagint vocabulary lists. This one (PDF) has all words that occur more than 100 times in the Septuagint. This list (PDF) includes words occurring more than 100 times in the Septuagint but less than 25 times in the New Testament. This second list is a good starting point for those who are (somewhat) proficient reading the New Testament in Greek, but who want to expand their reading into the more difficult (and larger) vocabulary pool of the Septuagint.