Stripe is a full-stack payment solution with very reasonable pricing and is easy to setup. See how to add it to a Rails application here. Currently only available in the US.
Here I show how to add PayPal recurring payments to an existing checkout process using PayPal's Express Checkout and the paypal-recurring gem.
(24 minutes)
Active Merchant is a great library for handling credit card transactions. In this episode I will show you the basics of using it to communicate with PayPal's gateway.
(10 minutes)