Amazon SQS is a distributed message queue system with a simple, robust API and real infrastructure to back it. And their prices just dropped significantly from a penny per 100 requests to a penny per 10,000:

Dear Amazon SQS Developers,

We wanted to let you know about some changes we are making to Amazon SQS, based on customer feedback and watching the way customers are using the service. One thing we’ve heard consistently is that customers want to be able to use SQS along with our other services (e.g. Amazon EC2, Amazon S3), but need SQS to be less expensive for this to be more feasible. We looked at our architecture and feature set, and found a way to make a few, targeted changes, by deprecating a few infrequently used requests, which allow us to operate the service much more efficiently. Simultaneously, we are introducing a new pricing structure that replaces the previous per-messages-sent charge ($0.10/1,000 messages) with a new per-request fee ($0.01/10,000 requests, including all Amazon SQS operations). The net result is that the new pricing will result in significantly lower charges for most developers being billed for SQS.

I’m hoping we’ll look back in five years and reminisce about how they charged so much for EC2 as well 🙂 (I do think it’s a good price now unless you are looking to continually use many, many computers).