CiviCRM is a popular open source CRM solution used by nonprofit organizations, charities, and other civic sector organizations. As such, it's important for these organizations to have payment processing options that are reliable, secure, and affordable.

There are several payment processor options available for CiviCRM, each with its own pros and cons. Here are some of the most popular ones:

1. PayPal: PayPal is one of the most widely recognized payment processors, and it's a popular choice for CiviCRM users. PayPal is easy to set up and offers competitive pricing. It also offers a variety of payment options, including credit and debit cards, PayPal accounts, and bank transfers. However, PayPal has been known to freeze accounts without warning, which can be problematic for organizations that rely on a steady stream of donations.

2. Stripe: Stripe is another popular payment processor that's easy to set up and offers competitive pricing. Stripe is known for its developer-friendly API, which makes it easy to integrate with CiviCRM. Stripe also offers a wide range of payment options and supports recurring payments. However, Stripe's fees can be higher than other payment processors, particularly for small transactions.

3. Authorize.Net: Authorize.Net is a popular payment processor that's been around for over 20 years. It offers a wide range of payment options, including credit and debit cards, PayPal, and e-checks. Authorize.Net is known for its reliable service and excellent customer support. However, its fees can be higher than other payment processors, particularly for small transactions.

4. iATS Payments: iATS Payments is a payment processor that's specifically designed for nonprofit organizations. It offers competitive pricing and supports a wide range of payment options, including credit and debit cards, PayPal, and direct debit. iATS Payments is also known for its excellent customer support and security features. However, it may not be as widely recognized.