I've had some great luck with Google Books [View all]
For so long, the only way a genealogist could find certain key information was to go to some local library, often far away, that had some obscure history or genealogical book. I have found some of these books digitized on Google books and many of them of free.
Recently I found a 3rd or 4th cousin through 23andMe and that got me interested in that particular branch of my tree. There were some obvious conflicts and a few unanswered questions that made me uneasy. Then I found a couple books on the town and the family in question AND it was free.
I've used Google books before but for some reason I keep forgetting about it as a resource. We've just moved to a small town in New Hampshire and I was curious about its history so I checked out Google Books. I found a 700+ page book free on Google Books and I was able to purchase it for my Kindle for only 99 cents. Now I'm wondering about all those "dead ends" on my tree and am anxious to revisit some old and neglected branches.