I’ve just finished adding Chegg.com as a new merchant. Chegg is primarily a company that rents textbooks to students, which is a farily new concept that seems to be gaining some traction. From what I know, they are a pretty good company to deal with and they seem to be offering a pretty competitive price for many textbooks. Please give them a try and leave feedback for them.
It looks like Powells also changed the layout of their page which broke lookups for it. That has been fixed, and I see that they now offer payment via PayPal.