Looks like Sage Pay is finally been added to the core code of osCommerce for RC3. Sage Pay was formerly known as Protx, and it is (and has been) the best 3rd party providers of Card services for the small merchant.
You can read more about Sage Pay at their page on the osCommerce website;
Probably the most popular is the “form” version, but if you are looking at going with Sage Pay, I highly recommend using Server or Direct. Both these are more professional, but only you can know what is right for your shop (and your pocket!).
Anywy, it’s good to see these added to RC3.