http://www.rightscale.com/

With the RightScale Cloud Management Platform, you can more easily deploy and manage business-critical applications on the cloud with new levels of automation, control, and portability. Whether you need a fast on-ramp to the cloud or support for complex deployments across multiple clouds, RightScale delivers.
Join the thousands of companies using RightScale to manage their applications on the cloud today.

http://www.rackspacecloud.com/

The Rackspace Cloud is the cloud hosting division of Rackspace, an industry leader that currently manages over 40,000 servers and devices for customers all over the world.

Cloud hosting is the next iteration of hosting. So, having the leader of managed hosting behind you is not such a bad thing. No doubt we benefit from tons of experience and knowledge, a great network, world-class data centers and the scale and backing of a company like Rackspace.

http://aws.amazon.com/ec2/

Amazon Elastic Compute Cloud (Amazon EC2) is a web service that provides resizable compute capacity in the cloud. It is designed to make web-scale computing easier for developers.

Amazon EC2’s simple web service interface allows you to obtain and configure capacity with minimal friction. It provides you with complete control of your computing resources and lets you run on Amazon’s proven computing environment. Amazon EC2 reduces the time required to obtain and boot new server instances to minutes, allowing you to quickly scale capacity, both up and down, as your computing requirements change. Amazon EC2 changes the economics of computing by allowing you to pay only for capacity that you actually use. Amazon EC2 provides developers the tools to build failure resilient applications and isolate themselves from common failure scenarios.