No doubt that one of the hottest topics these days are full text books online. I'm not talking about the Google Print or Search Inside The book material from Amazon.com type of content but the myriad of content out there FOR free (often, but not always, public domain stuff) that can be both interesting reading and useful research content. One source I've mentioned time after time on the SEW Blog, SearchDay, and ResourceShelf (it's that deserving) is the Online Books Page (directory really) from John Mark Ockerbloom at the University of Pennsylviania and has been online since 1993. This well organized collection is updated almost daily with newly digitized books. It collects materials from disparate sources.
I'm mentioning the OBP once again because its "What's New" list (material that's just been added to the directory) now offers an RSS feed. It's absolutely amazing just how much material gets added to the collection on an almost daily basis. This is one feed many of you will want to add.