PayPal/Amazon FPS intergration

I am looking for a web developer to help integrate a simple custom built shopping cart with PayPal and Amazon FPS (Flexible Payment Server). I would like the look and feel of the site to be implemented on the payment page as much as possible. I am very interested in hearing from coders that have had experience in integrating with PayPal or Amazon FPS (Flexible Payment Server) and any other credit card payment servers with no monthly fee, also where it is possible to customize the look of the payment page to match the site. It is would be helpful if you have knowledge of Java as the current shopping cart and the web site is built using Java/JSP technology but this is not essential. The work will be with the payment servers (PayPal and Amazon) and our coders can manage the Java side of the project. The site will is used for digital downloads for a mobile phone.