Yesterday the Internet Archive announced a new 80 thousand title eBook lending library which you can find on OpenLibrary.org. The IA also announced that it already has partners for this new lending library. Over 25 library systems across the US (with 150+ branches) have signed up to participate.
The Open Library Collection was developed in partnership with Overdrive, and you can borrow ebooks from Open Library through any participating library. A user can borrow up to 5 titles at once, and a loan lasts for up to 2 weeks.
For a list of participating libraries, please visit the IA blog.