How can I incorporate a payment processor in my web application?

One payment processor we've had success with is Authorize.Net, a 3rd party payment processor which claims to be the internet's largest payment gateway service provider.

Advantages of this solution include:

• a flexible API with detailed documentation and sample code
  
• secure transfer and storage of financial information
  
• accepts several methods of payment, including credit card and checking, with international currencies

In a lot of cases, you may need to use Authorize.Net's Automated Recurring Billing (ARB) API, which processes a transaction without the customer leaving the merchant's web site and provides subscription services to be leveraged by the software. The customer is unaware of how the transaction is processed and the checkout process is seamless to them. This method is usually chosen by businesses that wish to present their web site in a professional manner.

The ARB API should provide all necessary functionality for recurring billing, cancellation and error handling.

Authorize.Net sells its services to merchants both directly and indirectly through re-sellers (such as Chase Paymentech). You could investigate various re-seller pricing options. As well, resellers are typically merchant account providers, from which you may need to obtain a merchant account if they don't have one already.