http://www.religion-online.org/
Has a lot of Christian (and other religious) texts. Being in Religious Studies I've found this site very useful from time to time (and much of writers like Tillich are interesting for people of any religious persuasion). I've contacted the owner of the site about editing some of the content for distribution in free ebooks and he has no problem with it, but I'm not certain he has the rights necessary to say that.