Host Your Static Website on Amazon S3
Couple this with tools like Jekyll or nanoc (with JavaScript-powered comments, perhaps) and you can easily roll out powerful static sites that are dynamic locally. I can see this getting a lot of use because it makes it so easy to rig up new sites right from the shell. It was already pretty easy but the ability to create a new "site" by merely creating a bucket on S3 reduces the friction even more.(Perhaps too easy, even.. Rig up a domain registration API, content generator, and an S3 uploader and you could have a script pumping out auto-generated "content" sites all day without any hassles right from your terminal window.)