The reason I was looking into how to read a library book on my cybook is because I had been looking into online libraries. My local library probably won't even know what an ebook is for another 20 years, so I was looking for something widely available. Maybe this thread is a good place to list libraries people can use.
This is the best one I've seen so far, KnowBetter Lending Library. Limited selection but better than Fictionwise and apparently dedicated to growing. $19.95/year. Limited use available for free. Works with your fictionwise account.
There is also a lending library at Fictionwise, only available to their buywise club members (about $30/year but has other benefits). Very limited selection.