1. Regions.
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-regions-availability-zones.html
2. AWS Service Event.
http://aws.amazon.com/message/67457/
3. Rackspace Datacenters.
http://www.rackspace.com/about/datacenters/
4. EC2 Purchasing Options.
http://aws.amazon.com/ec2/purchasing-options/
5. Xen Credit Scheduler.
http://wiki.xen.org/wiki/Credit_Scheduler