PayPal is the next most reliable payment system for taking payments directly on your website. By reliable, in this context I am talking about the likelihood of success of the transaction. That is, when the customer will actually part with their money.
PayPal allows customers to make payment without creating a PayPal account (most of the time) and also offers them the option of paying with their PayPal account should they want to.
PayPal are known for their overly generous stance towards the purchaser against the retailer, and if you are using PayPal you should make sure you obtain verifiable proof of posting and delivery for every order, or be prepared to have the order refunded. In addition be ready for complaints from customers who are occasionally forced into a PayPal sign up process. And they are infamous for occasionally freezing accounts without specific explanation. Always empty your PayPal account either daily or when you have accrued the minimum free withdrawal...