Do be warned!
Using the above sites, and without proper reserve, you will have more books than you can read on your reader.
In fact I'll probably have a new and different ereader by the time finish all of my books.
And if you want to "borrow" books for $15 a year try;
The Free Philadelphia Library -- Available to city residents (free), anyone 65 or older (free), residents anywhere in PA with "Access Pennsylvania" library cards (free), and non-residents ($15)
Online Registration
DOWNLOADS: audio books, e-books, music, movies, plus.
Downloads Download Sampler
NOTE - You do not have to register in person. The first time that you want to remove "physical" material (books, movies, etc) you must show ID. Otherwise you can download audio books, e-books, music, movies, etc as soon as you get your library card.