I'm doing some research for an article and would like your help:<p>What startups and niches use payments or subscriptions as their primary revenue model?<p>The immediate one that comes to mind is groupon, but there are plenty of others. Like dating sites for example. Even 'service' sites like pandora.com fall under this.<p>What startups, niches or ideas can you think of that follow this revenue model? Please list as many as you can.<p>P.S. Lets leave out those that sell and ship physical products.