Avestan

From UniLang Wiki

Early Indo-European Languages Online A great site that has lessons in several Classical Indo-European languages, including Latin, Classical and New Testament Greek, Old Norse, Old Church Slavonic, Old Persian, Avestan, and Hittite. And the site keeps growing! It's run through the University of Texas.

Avesta.org Has a plethora of resources available on Zoroastrianism in general, and the Avestan language - including several lessons, and grammars.