Customers like options. Aside from that some customers prefer one payment type over another. Some customers only use PayPal while others only use Google Checkout. With this in mind you will want to integrate with as many Third Party Payment (TPP) providers as you can.
Some of the more popular ones are:
With PayPal you can offer standard PayPal payments with the customer sending you money via email with their PayPal account.
Another option is to utilize PayPal’s Checkout Express, where the customer does not need to enter any payment info on your site and they can just login to their PayPal account and checkout in 2-3 clicks.
In addition PayPal offers full credit card processing services (a la Authorize.net) where the customer does not even know that you use PayPal and it is fully integrated into your site.
Google Checkout is very similar to PayPal Checkout Express. It is pretty much the same easy checkout process which is done by logging into your Google account and going through 2-3 clicks to finalize your order. Google Checkout is popular amongst a small set of consumers specifically because of the ease of use.
BillMeLater, by CyberSource offers consumers the ability to checkout by providing their address as well as birthday and last four digits of their social security number. They do an instantaneous credit check and provide the customer with numerous options to pay for their purchase at a later date.
There are several companies that allow consumers to checkout via eCheck. What they do is ask for bank account holder information as well as routing and account numbers. One good thing about eChecks is that the consumer doesn’t have to wait the time it would take to mail in a check and have it clear as most companies that provide this service do a credit check and guarantee the funds.
http://www.echeck.net/ — by Authorize.NET
Amazon Payments is similar to Google Checkout and PayPal Checkout Express. The consumer goes through Amazon’s checkout process and does not need to provide the merchant with payment info.
Not sure how useful this would be to many consumers, but eBillme offer the ability to pay via your bank’s online bill pay option. The consumer pays eBillme and they route the money to the merchant.