Amazon has made public its Flexible Payments Service (FPS).  Amazon takes a set fee along with a cut of the transaction amount, which differs upon on the amount and payment method.  For example, Amazon charges 30 cents and a 2.9% cut on credit card transactions greater than or equal to $10 USD.  If you sign up before March 15 and launch your applications by June 1, you can take advantage of free payment processing for the first 90 days or $500,000 transaction volume.  Amazon provices a FPS Sandbox to build and test applications without using real money or incurring any transaction charges.