My public library has e-books for loan. MOBI, ebook, pdf, etc. Not all books come in all formats.
The loans are usually for 2 weeks, which is plenty time for an average book.
I interact with my library for ebooks exclusively online, which is awesome. Selection can be a bit limited, and it saddens me that the library stocks so many pot-boiler series and less Howard Zinn, but I can't argue with the price!
You download the book, put on the Kindle and it times out automatically in 2 weeks.