you could try
www.booksonboard.com,
www.kobobooks.com... inkmesh.com is a site that lets you search various sellers for an e-book. If you don't mind me asking, what sort of books do you think you would like to read on an e-book reader (genre, author)? It might help us steer you in the right direction if we had a list of authors that you like, for example, or the subject matter that you are most interested in.