However, there are many sites such as Project Gutenberg that offer free ebooks for you to download to your device for as long as you would like. If you have a NOOK you can buy ebooks from Sony eReader you can buy from their reader store. If you have a Kindle you can buy ebooks from.
This would include most new fiction ebooks. The paid ebooks are typically books still under copyright available in an ebook format.
On the internet, fiscally speaking, there are two types of ebooks you can download: paid and free.
The ebooks the library offers come with check out periods, so after a set period of time the books will be removed from your device unless it is an ebook with unlimited downloading capablity and no checkout periods. There is an important difference between the ebooks you can get off of websites and the ebooks the library offers.