Stripe Payment Gateway Module
Stripe is expanding beyond the US so demand for an official whmcs module will only increase. They have now expanded to Canada and looks like they will be available in Europe soon.
There is a commercial module available, however, I don't know how well that commercial module works but they currently want $45 per year which is rather expensive for what it is imho. On a product like whmcs which only charges around $140 a year that is an additional 30%. Every little bit adds up when you have to pay licensing for every little thing like this.