I'm a huge fan of +Free Library of Philadelphia and make use of a number of services. Yes, they have dead-tree books, as you would expect, but they also provide a range of electronic and online services, from e-books to streaming music and everything in between. Check out their Digital Media page for a complete list.
Check out this infographic to see what's available, and what is coming down the road from your public library. And keep in mind all this stuff costs, so if you find yourself with a spare buck or two in your pocket maybe help them out with a donation.