Whether linking a card or a bank account, if the donor only wants to enter credit card/account details once, she will have to create a PayPal or GMG account to store the account details to use in subsequent donations.
We have created custom PayPal implementations in the past, but we don't really do it anymore. Basically a programmer has to create a web-based form that has the options, and then pass that data to the PayPal checkout form.
Take a look at our Frequently Asked Questions page. It's a great place to start if you have questions. In the meantime, here are some common questions we get from customers.
There is a lot to consider when choosing your donation payment processor. You will want to determine which features are "must-haves" and which are "nice-to-haves" when making this decision. Each payment processor has its pros and cons, and in the end you'll have to decide which one best meets your fundraising needs.