Cloud Sites (which is $100/month) is a clustered, high availability hosting platform. I haven't personally used it, but based on my great experience with Cloud Servers, I'd expect it to be worth every penny.
Still looking for something as simple as a shared webhosting (mail and webserver work "out of the box", easy control panel) but with better performance.
RackspaceCloud.com sites is exactly this. You create sites, they come with uber-simple control panels, stats, email and databases. I really think you should look again at RackspaceCloud.com sites.
