I have recently discovered this website books.google.com
It is a great place to search for all kinds of books. If the book is an older one you can actually read it right there on the site.
I've started reading one of George McDonald's books there. It is a scanned copy of Malcolm from 1896. The Scots dialect is a bit difficult but I like the challenge of it.
His books are hard to find so I snatch them up when I come across them.
What out-of-print books do you wish they would republish?