Stripe.com
"Built for developers
Robust, clean APIs that let you focus on building great products."
Super easy, php code ready to go.
Here is a live example
require_once('./lib/Stripe.php');
Stripe::setApiKey("sk_test_BQokikJOvBiI2HlWgH4olfQ2");
Stripe_Charge::create(array(
"amount" =>...