I'm a big fan of Google Books. With a Google account, you can save Google ebooks to your library. The screenshot, above, shows what's currently in my own Google library. It is really pretty simple to use Google Books and you don't even to have a free account unless you want to keep stuff in the Google "cloud." Best of all, none of this takes up any storage space.
Below, you can watch a video on using Google Books for the beginner. One way I disagree with the narrator is that she is a big fan of picking "free Google ebooks." Personally, I like to switch back and forth, because for the "paid" or "paper only" versions, you can use the "find it in a library" which uses Worldcat to find what libraries might have the book so you can plan on getting a copy via interlibrary loan, or making a stop on your next trip.
Lisa Louise Cooke, the narrator, has a number of other pretty good videos that you can also watch via links from the one above, or by clicking here. She's got literally hundreds of these.
Another excellent video on using Google E-books is the one, below, which was narrated by Miriam Midkiff, a teacher from Spokane. Miriam makes the wonderful point that these old books can really help bring your ancestors to life.
"On Friday night, March 17, 1819, Henry Dale's house was robbed in a singular manner, the particulars of which we take from depositions taken before Judge Huston. Mr. Dale says, On that evening some person came near my house and hallooed. We were in bed, and got up and went to the door and asked what was the matter. He answered, Your son has killed himself. I asked, How? He said he had his powder-horn, and it caught fire and tore him amazingly all to pieces; if you do not hurry, you will not see him alive."and the story goes on for another full page. The son was Samuel Dale. And no, Samuel hadn't died - it was just a scam to get Henry to step out so his house could be robbed.
Introduction to Google Books
Part 1 - Genealogy Research Using Google Books - this post
On to Part 2 - How To Find & Use Google Books For Genealogy Research - Lisa Lisson adds more details and another video
On to Part 3 - Secrets of Printing from Google Books - There are several ways to print from Google Books - this post covers five of them