I use http://saasy.com http://saasy.com because I am in Canada, if I was in the USA I would use stripe.com. It depends on how much you're charging too - chargif

I use http://saasy.com http://saasy.com because I am in Canada, if I was in the USA I would use stripe.com. It depends on how much you're charging too - chargify looks good, but actual costs are $3.49/user... and up to almost $10.