It's called Bookswim, available at http://www.bookswim.com/ , and I have no idea whether it's good, because I cannot conceive of using them over the library.

Ask your local library system about interlibrary loan. You may have trouble with books released in the last 6 months (it's peak borrowing time, libraries like to hold them for their local patrons), but otherwise you can get basically everything.

I'd like to be notified when authors have new book coming out. You get this from some publishers, but what if the author jumps to another publisher?

Add in graphic novels and I'm in. It would have to emphasize breadth and new releases to make it clearly superior to the local library.

Yeah libraries are awesome. I grew up going to the library. That does mean that I am used to not spending money on books. I usually only buy a book if it is going to be read more than once and I know will find it useful. So I really want full access to the book before I decide to spend money on it.

This is an interesting thought. Does anything already exist as a service for college students to rent textbooks?

While access to textbooks would be nice, it wouldn't need to be a major selling point. If the book is for a class in my major, I want to own a copy so I can use it as a reference after the class is over. And used textbooks can be had for a decent price. I just paid $40 including expediated shipping for a circuits book. The book is in great condition, and I am happy with my purchase.

And renting textbooks is pretty expensive, especially for older books. I bought a different used textbook for around $15. The book is in great condition, and renting it would have cost $40.

It would be hard to maintain, since a lot of textbooks change version number relatively frequently.

Yes, there are quite a few, actually. But they usually don't give you significant advantages over the old buy new/sell used model.