We love the guys at Stripe, they have an awesome product. They provide a super simple gateway for developers. WePay provides super simple tools for anyone (mostly non-developers) to accept payments.

We LOVE to see innovation in user experience disrupting the payments industry from the likes of Square in mobile POS, Stripe for developers, BankSimple for checking accounts and WePay for SMBs & non-profits.

I should mention that we offer an API, but it's mostly for folks that want to allow their users to accept payment via their site (i.e. for marketplaces, fundraising tools, or event planning) - it's not really for recurring billing or merchant processing like Stripe. For more information, see wepay.com/developer