If you subscribe to LISNews, you may have seen the Prelinger Library already. The reason it was highlighted at LISNews is that in its May 2007 issue Harper's wrote about the "appropriations-friendly" library, which exists physically in San Francisco and virtually on the Internet with 2098 books. The Prelinger is a research library that free for anyone to use and holds many unusual items. The focus is "landscape and geography; media and representation; historical consciousness; and political narratives from beyond the mainstream." It sounds like a nice place to spend an afternoon.
Right now it is the free to view eBooks that impress me. Take a look at The Bird Book by Chester A. Reed (1914). On the left of the description page is a box with viewing options. I really like the simplicity and easy use of the flip book version, which is much nicer than netLibrary books, but the display is a little small. The DjVu version has a larger display and works almost as easily. Both version make reading a book from a computer with a 17-inch monitor possible. Avoid the PDF version, which takes a long time to load.
There are many items that will interest readers of history. Having grown up in Texas, I might want to come back and read Sam Houston: Colossus in Buckskin. (Maybe not, as it glorifies Houston without criticism.)
It looks as though the online library is really a collaboration with other online collections. The digitization of the book I chose may not actually have been Prelinger Library work, as there is an Internet Archive logo in the top left corner of the webpage and links to other institutions in the navigation. For the reader, the origin of the book probably does not matter. The Prelinger Library website provides the portal.
I am making a bookmark.