Rackspace Cloud Sites

Rackspace Cloud Sites is a robust platform-as-a-service (PaaS) hosting cloud built for easily deploying and scaling static and dynamic web applications built on PHP or ASP/.NET. It supports inherent scaling and redundancy via load-balancing apps across multiple servers and supports two popular database back-ends (MySQL and MS SQL Server).Cloud Sites automatically balances your traffic across an entire cluster of servers. It's web hosting without the hassles of managing a dedicated server or the poor performance common with shared hosting. Just code it, load it and watch it scale.

See the reference side-by-side comparison Platform as a service (PAAS) for cloud applications (Scalable cluster of services)