Google Books: Actually Useful
I've been finishing up my revised edition of Tolkien's Beowulf and the Critics and have cleaning up the section where I identify of all the "voices" in Tolkien's "Babel of Voices," where he presents the history of Beowulf criticism.
In doing all the necessary but tedious i-dotting and t-crossing, I've found Google Books to be remarkably helpful for nineteenth-century Beowulf scholarship. They have full text of a lot of important but hard-to-find books (hard to find because Interlibrary Loan isn't often willing to send books published in 1840), and the interface and mark-up is much better than I remember it being.
I'm still not a fan of Google Scholar, which seems incredibly random in its selection of material, but Google Books seems to be not only a copyright grab but also a useful resource.