I reviewed sites in the past to load your Kindles, nooks, and Androids. Some include:
What is needed now, is a good search engine. Have no fear–find one at search-ebooks.eu. Obviously a European based site, but a site with a wide variety of content. They mention they add 200,000 new books a day. Their terminology may be a little different than stateside, as .xls, among other file types, do not necessarily denote eBooks, but they do possess lots of .pdfs, .docs, .txt, .ppt, and the aforementioned .xls.
They definitely do possess *links* to a wide amount of content. I say links, as they very clearly want to show they do not store these documents, but link to the various sites across the net. Very important these days as the crazy yahoos running the MPAA, RIAA, publishing companies, and all around 1% would want to sue anyone hosting content into the ground.
You will find offbeat content, but offbeat in a way that may not be bad. For instance, a search for Moodle found many tutorials created by any number of people in any number of situations. From a classroom teacher to a technical college, you will find a wide range of content. Definitely a great place to find content!