Beliefnet‘s online library of sacred texts includes all the usual suspects, plus rare finds such as selections from the Poetic Edda, a collection of mythic and heroic poems from thirteenth- and fourteenth-century Iceland.
Bible Gateway offers a searchable Bible, in multiple editions, by word or citation.
Internet Sacred Text Archive is a great source for scripture from a few dozen world religions. Complete texts (including different translations) of the Bible, Tanakh, Koran, the Vedas, basic Buddhist works, Bullfinch’s mythology, the Book of Mormon, Thomas More’s Utopia, etc., etc.
JewishEncyclopedia.com “contains the complete contents of the 12-volume Jewish Encyclopedia, which was originally published between 1901-1906. The Jewish Encyclopedia, which recently became part of the public domain, contains over 15,000 articles and illustrations.”
Saganet is a beautifully produced site from Cornell and the University of Iceland that offers searchable access to the texts contemporary Pagans are using to build their religion. “The material consists of the entire range of Icelandic family sagas. It also includes a very large portion of Germanic/Nordic mythology (the Eddas), the history of Norwegian kings, contemporary sagas and tales from the European age of chivalry.” Plus, there’s a picture of the world’s fattest book.