Yes, Paypal is the most common. I have seen one that used Google checkout and I have registered for that, but only used it once. Moneybookers or egold seems to be used a lot by those in Europe. NP$ is not a bad option if the amounts are small and you are buying and selling a lot. I had one seller that doesn't have PP in his country ask me to buy a Godaddy gift card to pay him for a domain I bought.