You people! Always wanting more!
You can do an installation on the cloud if that's what you wish. There are many providers that offer cloud services and that will allow you to work in the cloud while making it look as if you were using only one server. So installing WP there shouldn't be much of a problem. And of course that includes Amazon. Little tutorial here http://wp.tutsplus.com/tutorials/scaling-caching/deploy-your-wordpress-blog-to-the-cloud/
Rackspace even offers a cloud hosting service with WP installed.
Now, if you want to do a regular installation but save your files (post pictures, videos, audio, or files) in the cloud, you can use a WP plugín. You can search WP repository to find the one that suit you best. As an example, SMEStorage has one or two plugins related with saving files in the cloud.