Google Checkout is one of the largest and most recognized internet credit card gateways in the United States.  Thru Google Checkout, you can submit your payment using Mastercard, Visa, Discover Card, or American Express.

Google Checkout allows you to set up an account.  This way you only have to enter your credit card information once.  After that, you can just log in when asked for payment using the user name and password you set up initially.  To set up an account now, just click on the Google logo above.