There a great list of public domain Greek grammars available here for download. Head on over for the following:
Blass, Friedrich. Grammar of New Testament Greek. Translated by Henry St. John Thackeray. London: Macmillan & Co., 1898.
Buttman, Alexander. A Grammar of the New Testament Greek. Translated by J.H. Thayer. Andover: Warren F Draper, Publisher, 1891.
Goodwin, William W. A Greek Grammar. Revised ed. Boston: Ginn and Company, 1892.
Moultan, James Hope. A Grammar of New Testament Greek. Vol. 1 Prolegomena. Edinburgh: T&T Clark, 1906.
Nunn, H.P.V. A Short Syntax of New Testament Greek. 2nd ed. Cambridge: Cambridge University Press, 1913.
Robertson, A.T. A Grammar of the Greek New Testament in the Light of Historical Research. 3rd ed. London: Hodder & Stoughton, 1919. This is not page scans but a pdf file created from an electronic copy.
Smyth, Herbert Weir. Greek Grammar for Colleges. New York: American Book Company, 1920.
Ted Hildebrandt also has a collection available over here. I won’t list them all because he has provided a full bibliography.
You can also find these related lexicons on Google:
Bullinger, Ethelbert William. A Critical Lexicon and Concordance to the English and Greek New Testament: Together with an Index of Greek Words, and Several Appendices. Longmans Green, 1908. Download.
Parkhurst, John. A Greek and English Lexicon to the New Testament: In which the Words and Phrases are Distinctly Explained, and the Meanings Assigned to Each Authorized by References to Passages of Scripture, and Frequently Confirmed by Citations from the Old Testament, and from the Greek Writers. London: T. Davis, for J. Johnson et al., 1809. Download.
Robinson, Edward. A Greek and English Lexicon of the New Testament. New ed. London: Longman, Brown, Green and Longmans, 1850. Download.