For those who would rather own a copy instead of borrowing the images and links will take you to booksellers.

Barnes and Noble has a large selection of mostly new books. Check out their sale annex where you can get new or in new condition books for less than $10.

For a wide selection of used and hard to find books try Alibris. They are mostly a network of independent bookshops. Often they don't have the ISBN of books so you have to do a keyword or title search and then pick through a list of unrelated books to find the one you want.

Willman Bell publishes alot of independent astronomy books as well.