Amazon Web Services just announced Cloudfront CDN.

Amazon CloudFront is a web service for content delivery. It integrates with other Amazon Web Services to give developers and businesses an easy way to distribute content to end users with low latency, high data transfer speeds, and no commitments.
Amazon CloudFront delivers your content using a global network of edge locations. Requests for your objects are automatically routed to the nearest edge location, so content is delivered with the best possible performance. Amazon CloudFront works seamlessly with Amazon Simple Storage Service (Amazon S3) which durably stores the original, definitive versions of your files. Like other Amazon Web Services, there are no contracts or monthly commitments for using Amazon CloudFront – you pay only for as much or as little content as you actually deliver through the service.

Cloudfront has a calculator too.

Here is the AWS blog entry on Cloudfront.

Like all of our other services, CloudFront was designed with ease of use in mind from the very beginning. There are no minimum usage commitments, no monthly fees, and no need to even talk to us. Here's what you do:

Sign up for CloudFront.

Put your most frequently accessed static content into an Amazon S3 bucket and mark it as publicly readable.

Create a new CloudFront Distribution using a single REST-style POST call. Capture the domain name returned by the call.

Generate fresh URLs for your content using the domain name from step 3 and hand them out. By using our CNAME support you can even make the content appear as if it is coming from your own domain. You can associate up to 10 CNAMEs with each distribution.