The PHPBuilder.com site has a tutorial posted helping you integrate Stripe into your PHP application as a payment gateway service.

Stripe is a payment gateway that is becoming increasingly popular in the Web industry. It offers payment processing services, which can be easily integrated into your Web application using the Stripe API.

Although it is not free (2.9% + 30 cents per transaction), Stripe saves time and reduces cost in many ways: seamless integration and good documentation reduces the amount of time and development hours needed, while it offers complete control over sensitive data which saves hundreds of thousands of dollars that would otherwise be spent on ensuring PCI compliance.

They then show how to set up and use the PHP Stripe API package to create a simple checkout form to accept credit card information and use the stripe.js handling to send it directly to Stripe. Once the service receives it, it then makes a call back to your callback endpoint to create a token value for the transaction and customer. This callback then uses the API to make the actual charge using the token for the payment method and the customer information.

On NetTuts.com there's a tutorial showing you how to use the GoCardless service to accept payments on your site (in the UK, unlike some other online payment services).

Online payments are increasingly becoming more and more popular. GoCardless is yet another payment service, which currently works in the UK, allowing you to accept payments online.

Most of the tutorial is used to explain what the service is, getting you set up with an account (complete with screenshots) and how you can work with their API via an SSL connection. Included are examples of this using their PHP Library and what the results look like in their interface.

On NetTuts.com they're posted a new tutorial about using the Stripe service to accept credit cards on your site. Thanks to some handy libraries they provide, integration is a relatively simple process.

Until recently, accepting credit cards on a website was expensive and complicated. But that was before Stripe: a radically different and insanely awesome credit card processing company. Today, I’ll show you how to start accepting cards in 30 minutes or less – without spending a dime.

They step you through the whole process you'll need to get the full flow set up:

• Install an SSL Certificate (on your server)
• Create an Account
• Create Your Payment Form
• Collect The Form Values
• Request a Token
• Create a Server-Side Script

Screenshots of the Stripe interface, HTML, Javascript and PHP code are all included - everything you need to make the simple card handling work. One of the keys to how Stripe deals with credit cards is that you provide it the card info, it gives you a token. Your app uses this to work with the card instead of storing the card information in your database (also making it more secure).

NetTuts.com has a new tutorial posted today about processing payments with PayPal using their "Payments Pro" API and a handy library that makes it pretty simple.

While one of its most popular features is the ability to simply sign in to your PayPal account to submit payments, merchants using PayPal can also accept credit cards directly just like a traditional merchant account solution would provide. PayPal calls this solution Payments Pro, and I’m going to show you exactly how you can process credit cards directly with PayPal’s API using their Payments Pro web service API’s.

They've broken it up into the different steps including:

• Setting up the configuration
• Creating a first API request
• Sending the HTTP request to the PayPal API (via curl)
• Parsing the response

The Zend Developer Zone has posted the next article in their OXID and Authorize.net series (part one) focusing on the setup and application code to accept credit card payments.

Over the next couple of pages, I'll discuss this in detail, showing you how to create an OXID eShop module to accept credit card payments via the AlertPay payment service. Unlike Authorize.Net, this service requires users to visit and enter credit card information into a third-party Web site. As such, integrating it with OXID eShop is somewhat more complex, but it can be done.

The tutorial includes not only the description of how to make it work but also sample code and screenshots to ensure it's easy to follow each step of the way. There's lots of content here and plenty of steps to follow.