Stripe and Recurly seems like the best choices for recurring billing but what about non-recurring billing? Most of our users will be paying once. What's the best solution in term of good API balanced with decent transaction fees? Preferably with merchant accounts as we don't have one and available in Canada and US...
Though they don't support Canadian vendors yet, I would keep a very close eye on Stripe. Their API, support and overall attitude are kick ass and a breath of fresh air.