Since 2010, to my surprise I began to write occasionally about payment systems, including
Rosston Meyer attractively lists Online Payment Systems pertinent to US site developers. VentureBeat highlights New Relic's 2012 study here. I very much admire the reporting job done by StorefrontBacktalk's Payment Systems sub-section.
Among the many entertaining articles that make their way to IEEE Spectrum, "There's no stopping the rise of e-money", "The Beginning of the End of Cash", "Phone-y Money", "The High Costs of Taking Your Money", "The Long Life and Imminent Death of the Mag-Stripe Card", and "No More Waiting on NFC" bear directly on payment systems.