On his blog Chris White explains how to upload files directly to S3. Pretty cool!

Most of us know of Amazon S3, a cloud based storage service designed to store an unlimited amount of data in a redundant and highly available way. For most situations using S3 is a no brainer, but the majority of developers transfer their user's uploads to S3 after they have received them on the server side. This doesn't have to be the case, your user's web browser can send the file directly to an S3 bucket. You don't even have to open the bucket up to the public. Signed upload URLs with an expiry will allow temporary access to upload a single object.