AWS CloudFormation

AWS CloudFormation gives developers and systems administrators an easy way to create a collection of related AWS resources and provision them in an orderly and predictable fashion.
With CloudFormation, you can start and stop an entire environment with one operation.

It’s very similar to Microsoft Azure’s approach with their .cscfg and .csdef files which are an analogous XML model – you really could fairly call this feature “Amazon implements Azure on Amazon” (just as you could fairly call Elastic Beanstalk “Amazon implements Google App Engine on Amazon”.)
Amazon CloudFormation: Model Driven Automation For The Cloud

There is one nasty thing at the moment is that there is no support for Spot Instances in the CloudFormation 😦

UPDATE: Using CloudFormation Templates to Launch Spot Instances

Amazon EC2 Spot Instances for Acceptance Testing

Using Spot Instances can reduce costs by at least two times as compared with On-Demand instances.
On-Demand (Large): $0.48 per hour
Spot Instances (Large): $0.20 per hour

Set your maximum price near to the current Spot Price. If the Spot Price goes above your maximum price and your instance is terminated by Amazon EC2, you will not be charged for any partial hour of usage. Just imagin, you have completed the tests in 30 minutes and the instances are termintaed by Amazon EC2. You will get testing for free.

BTW: Do not tell anyone about this;)
Spot Instance
Have requested the large instanse for maximum bid price $0.250. You will often pay less per hour than your maximum bid price. The Spot Price is adjusted periodically as requests come in and available supply changes. Everyone pays that same Spot Price for that period regardless of whether their maximum bid price was higher. You will never pay more than your maximum bid price per hour.