Thanks to Jim West for news of this new resources:
Live Search Books
Like Google Books, it has plenty of public domain books in full view downloads available. I've not had a lot of time to play with it yet, but time enough to find the following, which is not available on Google Books:
J. C. Hawkins, Horae Synopticae (Oxford: Clarendon, 1899)
The quality of the scans seems very good, and the site seems pretty easy to use. So thumbs up so far, and I am looking forward to searching for more.
Update (Tuesday, 10.05): Thanks to Ken Olson for pointing out that this is in fact the first edition of 1899 (see comments), so I've adjusted above.