I've written a subscription based web app that I want to charge (by credit card) a monthly fee. There are 3 different plans and once they sign up, they should be billed that amount, automatically, every month until they cancel. Is there an easy way to set this up (some sort of online service maybe?).
You can use Paypal's merchant service to provide reoccurring charges for a subscription. Pretty easy to implement, they provide plenty of examples and even a sandbox to get you up and running.