Introductions to the Septuagint (LXX)
The Septuagint Online (A superb starting point for LXX studies)
Introduction to the Old Testament in Greek by Henry Barclay Swete (2nd edition.
Grammar of Septuagint Greek: With Selected Readings, Vocabularies, and Updated Indexes by F. C. Conybeare Complete text (Find the page for the section you want to read and then enter that page number in the address immediately after “greekgrammar&page=” and before “&view=png”)
The Old Testament in Greek edited by A. E. Brooke, N. McLean, and H. St-J. Thackeray. (London : Cambridge University Press, 1906-). LXX text with critical apparatus for Genesis-Ruth.
To navigate through these volumes I recommend estimating the appropriate page number and placing it in the address in the place indicated: http://www.ccel.org/php/disp.php?authorID=swete&bookID=lxx1&page=[page number here]&view=png)
Invitation to the Septuagint by Karen H. Jobes & Moises Silva
The Septuagint in Context: Introduction to the Greek Version of the Bible by Natalio Fernandez Marcos, Wilfred G.E. Watson
The Use of the Septuagint in New Testament Research by R. Timothy McLay