While poking around in Google Books, I have just discovered that the wonderful Merriam-Webster's Dictionary of English Usage is available in full text mode. As far as I'm concerned, this is one of the few really worthwhile usage guides. Unlike most of the bozos who opine about how you should or should not write, the Merriam-Webster's folks actually look to see how reputable writers actually use language instead of just spouting off based on their personal whims, and they show a deep knowledge about the variety of opinion on various points of usage. Merriam-Webster deserves kudos for making this invaluable reference work fully available on line. The only thing you can't do is download a pdf copy, but when you compare the accessibility of this work to the normal Google Books display of works in copyright (either a limited preview of a few pages or the practically worthless "snippet" view), I'm not complaining.