Amazon Queue Service
The Amazon Simple Queue Service is now available for beta testing. The Simple Queue Service offers a reliable, highly scalable hosted queue for buffering messages between distributed application components.
You can use the Amazon Simple Queue Service to better manage messages between components of your distributed applications. SQS allows you to decouple components and make them run independently. Any component of a distributed application can store any type of data in a reliable queue at Amazon.com. Any other component or application can then later retrieve the data using queue semantics. The queue acts as a buffer between the work-producer that is saving the data, and the work-consumer that is retrieving the data for processing.
Registered developers can create any number of queues. Each queue can hold up to 4,000 items and each item can be up to 4,096 bytes in length.
The Amazon Simple Queue Service is free at this time. We [Amazon] anticipate charging for this service once it is officially released. We [Amazon] haven't finalized pricing yet, but we expect to make this service available to you at a very reasonable price.