The natural way to learn ancient Greek is to start with the attic dialect and with some texts from Plato and Xenophon. With some basic knowledge in this standard language, one can learn the dialects, the epic and poetic language and the koine (e.g. New Testament) by comparison. The most radical way is to learn at the start only what is absolutely essential of the attic dialect, that is the way of Kaegi’s elementary grammar:
http://www.archive.org/details/ashortgr ... 00unkngoogThere are several new editions up to our time, and the essence of this book is really good because Kaegi made statistics and teaches only, what really occurs in the most important writings of the standard authors. The contrary is the grammar of K.W. Krüger which is available only in German:
http://www.archive.org/details/griechischespra03krgooghttp://www.archive.org/details/griechischespra04krgoogHe treats the attic dialect in the first part and the epic language and other dialects in the second. Good, but very detailed and a little unhistorical (I use this as a reference grammar, bound with white pages for remarks).
The other grammars treat the whole grammar in its historical development, mostly in a selection for the use of schools. My favorites are:
Raphael Kühners larger grammar (the German version is the standard for scientists):
http://books.google.com/books?id=7wsAAA ... &q&f=falseGeorg Curtius’ grammar for schools (very consequent in its historical and comparative approach):
http://www.archive.org/details/students ... 00curtuoftButtmanns larger grammar and the shortened school grammar (the first grammar of modern standard):
http://www.archive.org/details/drphilip ... 00buttgooghttp://www.archive.org/details/agreekgr ... 00robigoogVery apt for librivox would be in my opinion one of the shortened versions of Kühners grammar, one from Taylor and the other from O’Leary:
http://www.archive.org/details/anelemen ... 04taylgooghttp://www.archive.org/details/anelementarygre00olegoogFor the New Testament, the best modern special grammar of Blass/Debrunner is not PD, but there are two excellent alternatives from Winer and Buttmann (the son):
http://books.google.com/books?id=xgMVAA ... &q&f=falsehttp://www.archive.org/details/greekgra ... 00trolrichAt last, I might mention something special, the Latin book de praecipuis graecae dictionis idiomatismis from Francois Viger (1590-1647), which is to my great astonishment also available in English:
http://www.archive.org/details/depraecipuisgrae00vigehttp://www.archive.org/details/vigersgr ... 00vigeuoftThis book is quite dubious in concept and content, and the notes especially from Zeunius not trustworthy, but the remarks of Gottfried Hermann are great. So this book is a document of the great progress of science during the 18th and early 19th Century.