Over the years I’ve stumbled across a few caches of Rabbinic Writings on the web. The Talmud Yerushalmi & Bavli along with the Mishnah are available at Mechon-Mamre. David Instone-Brewer of Tyndale House has pointed out that Tsel Harim has made available the Midrash Rabbah in Hebrew. I found that they also have the Midrash Tanhuma, and the Yalqut Shimeoni. By chance, I stumbled upon the Seder Olam Rabbah, available at Shechem.org.