The day is coming when all serious research will be done electronically in whole or in part. The medium surpasses paper in various ways. To be sure, the potential of the electronic medium has yet to be fully exploited. A fine example of what can be done is Steve Mason’s Project on Ancient Cultural Engagement, which majors in Josephus and Polybius.
Three online encyclopedias are particularly helpful for the study of the textual worlds of Judaism and Christianity.
The Jewish Encyclopedia (1901-1906). JE. If the site is down, the entries are still available in less helpful form at Bible Wiki. The more recent and now updated Encyclopaedia Judaica (11972, 22006), not available free online, supplements but does not replace it.
Wikipedia: The Free Encyclopedia. A work in progress. It often excerpts and condenses entries from JE and CE. Occasionally, the entries are excellent.
In the field of Judaica, three sites provide superb access to primary sources in Hebrew and Aramaic.
Mechon Mamre. Tanakh, Targum Onkelos, Mishnah, Tosefta, Talmud Yerushalmi, Talmud Bavli, and Rambam’s Mishneh Torah. Also available: The 1917 JPS translation of the Tanakh. Coming online: a bilingual edition of Mishneh Torah.
Sifrut haQodesh. The same Hebrew and Aramaic texts found on Mechon Mamre, plus Midrash Tanhuma.
Seforim Online. A wealth of Judaica in PDFs. Examples: Saadiah Gaon’s Emunot veDeot; Rambam’s Guide for the Perplexed in Arabic, Hebrew, and English; the Divan Shmuel HaNagid; C. D. Ginsburg’s The Massorah (6 vols.); M. Friedländer’s Essays on the Writings of Abraham ibn Ezra; Shirei Moshe ibn Ezra (2 vols.); Shirei Shlomo Ibn Gabirol (5 vols.).
For the Bible in Greek, one site is particularly helpful.
The Resurgence Greek Project. Fully tagged and accented Greek Old and New Testaments.
For an incomplete but still helpful range of Greek and Latin works, one site is helpful.
My hope is that all Jewish and Christian classics will be “Libronixed” in the coming years. Those familiar with the Libronix system know well what a blessing it is to have a reference tool within the Logos Library.