PayPal is the world’s most widely used payment acquirer, processing over $4 billion in payments in 2011. PayPal payments are made using a user’s existing account or with a credit card. Money can be sent directly to an email address, thus prompting the users to sign up for a new PayPal account. In addition to taking payments, PayPal also allows its users to send money through the service, which is a feature that only a few payment solutions provide.
Pricing: PayPal takes 2.9% + $0.30 per transaction and has no setup or monthly fees. Source: PayPal merchant fees