At UK-based Make Your Offer, indie authors can sell their ebooks in multiple formats. What’s new, here? At MYO, the author stipulates a sale price and then either permits or does not permit lower bids from interested readers. For instance, you might list your book for sale at $2.99, receive a bid from a reader of $1.99, then counter-offer at $2.29, whereupon the reader accepts and you make the sale. You can either set things up to run automatically by inputting a minimum acceptable price, or you can entertain any offer. You can also offer books for free.
Books enrolled in Amazon’s KDP Select program can still be listed on MYO for promotional purposes, though readers will not be able to purchase the book through MYO.
From what I can tell, authors will generally keep a markedly higher percentage of the book’s selling price than the percentages offer by Amazon:
14. The Distributor will pay the Owner the full selling price of the Work for all copies sold through the MakeYourOffer Internet website, always subject to the following:
(i) The deduction of the payment processing fee at cost from the payment processing agent;
(ii) The deduction of a sales fee of five  per cent. of the total full selling price of the work. (http://make-your-offer.com/book_upload_terms.php, accessed 5/4/12)
Sounds to me like an exciting innovation in indie ebook sales. Cool.
**Edited 5/6/12: MYO’s administrator posted more specifics about royalty structure in the comments to this post. Looks like a 61% royalty is as low as it gets, at this time — quite a bit better than Amazon’s lowest threshold of 35% — and it could get quite a bit higher than 70% for more expensive books.