PayPal.com has one of the easiest, biggest, most secure, and best online buyer / merchant services around, and is available in multiple countries. It's free to register a personal or business account, and buying services are free too (other than PayPal credit services). Business merchant fees are about 30 cents plus 2.9% per credit card / PayPal payment received.

 It can be used to send a friend money or safely buy online even if one doesn't have a credit card (if bank transfers are available for your country through PayPal), as well as used to process any customer's credit card payments (no account is required for the customers paying via credit card). Direct bank deposit and withdrawal between bank accounts and PayPal accounts is available in some countries too.

 eBay.com bought them in October 2002, and they have grown to be an industry leader in online merchant accounts (in fact, they already were beforehand).