PayPal is the preference, from a convenience and security point of view. Although they do take a cut, using them as a payment provider means they handle all the difficult and secure stuff. The website is immediately informed of any contributions and your membership gets updated automatically.
The alternative would be a bank transfer. I've published the international bank account number on the Membership page. Please use the reference numbers shown there so I can identify where contributions have come from. These are unique to your account. It'll be DON and a number, for one off donations, or SUB and a number, for regular contributions.