We love NationBuilder and all the built-in integration it offers its users. One of the places where it shines is in the donation department. For those candidates and organizations that would like to accept donations and other payments directly through their NationBuilder site, there are a few different options for integrated payment processors.
For those folks in the US, NationBuilder integrates with Authorize.net, as well as Democracy Engine. We like Democracy Engine a lot for our clients - the interface is straightforward, and you don’t need a merchant account at your bank to start accepting donations right away. Authorize.net offers a very nice integration as well.
NationBuilder also integrates with SagePay and the ubiquitous PayPal and PayPal Payflow Pro. Users should note that the integration between PayPal and NationBuilder is such that donors are required to input their information into a donation form on your Nation, only to be redirected to PayPal and asked to input their login and credit card information once again. This poses a significant extra hurdle to potential donors. It inevitably will decrease your conversions and should probably be avoided when at all possible.
See the official NationBuilder documentation on payment processor integration can be found here.