Ask HN: Best data-store service with a JSONP/CORS REST API?

I've got a few client-side apps in JavaScript and I'm looking for a place to store the data. I don't want to run my own persistence API for every one of these little experiments, but I need to have access to the records they create, so I can't use localStorage.

I'm aware of Amazon S3[1] and I'm also looking at MongoHQ[2]. They both have a REST API, but I'm not sure they support JSONP or Cross Origin Resource Sharing. Do you know of any data-store service with an API like that?

Thanks