We don't normally feature websites, but I have been locating so much information on Google Books that I thought it worth mentioning.
Google Books has digitized thousands of books and allows users to search them using OCR (optical character recognition) technology. I've found many pieces of information I was unaware of, including the fact that a great-great-grandfather's brother-in-law was a chronic alcholic and that his son was mentally incompetent, but I digress.
I have been searching http://books.google.com for either some of my more unusual last names or just typing in ancestral names. Not all books are completely online, but there will be links with citation information so you can try and get a copy of the book yourself, either by purchasing it or obtaining it on interlibrary loan.
Of the books that are completely scanned and on Google, you can download them as a PDF or text file. I prefer PDF. But keep in mind, the "search" in Adobe Acrobat Reader is not the exact same search as in Google books. Google books found "troutfetter" in a book (and I saw it, so it was there). I downloaded the book and then viewed the PDF file and had that program (Adobe Acrobat Reader) search the file. Adobe didn't find it. So now I'll make certain and make notes about the page numbers before downloading the entire file to my computer.