The remarkable resource that is Textkit has added several major new full-text, on-line books. As with everything on Textkit (I think?), these new resources are PDFs that can be downloaded for free. Resources are usually out-of-copyright old-fashioned stuff, but often really useful. These new resources have just been announced on the Greek part of the site. Descriptions below taken from the Textkit site:
Sidgwick's Greek Prose Composition Key, Arthur Sidgwick
Learn Greek with this classic Greek Prose Composition key by Arthur Sidwick. The key, in Classical Greek, can be used to check your work against the lessons presented in Sidgwick's Greek Prose Composition.
A First Greek Course, Sir William Smith
Download this free first year Greek book. Sir William Smith's A First Greek Course was popular throughout the United Kingdom from about 1867 through 1960
Pocket Lexicon of Greek New Testament, Alexander Souter
Download this free and very handy New Testament Greek Lexicon. At 297, the Greek to English lexicon presents key New Testament Greek words with English meanings.
The Gospel of St. Luke in Greek, H.R. Heatley
Download this free New Testament Greek reader of the Gospel of St. Luke. This reader provides the St. Luke's Gospel in Greek along with line notes and a helpul vocabulary to assist the Biblical Greek learner.