Scalable Applications—You can build a scalable application that shrinks or expands to meet your current demands.

This can help you use only the compute resources that you need and can help you respond to events where a mention on a popular news site can result in a dramatic spike in traffic.

Temporary Events—You can use Amazon EC2 for temporary solutions and one-off events that would require you to maintain a fleet of compute resources that are normally idle.

This includes hosting conferences in virtual worlds, live blogging, distribution of newly released media, and short-term promotional websites.

Batch Processing—You can use Amazon EC2 for projects that require massive compute resources which would be expensive to build on your own.

This includes video and image processing, financial data processing, and science and research applications.

Fault Resilient Applications—You can build an application across multiple availability zones which will be protected against the loss of an entire physical location.