Clouds

Non open-source / Not Free

• Amazon AWS (aws.amazon.com)
• Microsoft Azure (http://www.windowsazure.com)
• Zunicore (https://www.zunicore.com, made by peer1hosting.co.uk)
• ElasticHosts (http://www.elastichosts.com)
• CloudSigma (http://www.cloudsigma.com)

Some performance real-time comparison: https://cloudsleuth.net/global-provider-view?utmp=cs_web_app_250x150_DETAIL_40_CLOUDSIGMA_-_LAS_VEGAS_NORTH_AMERICA_30D

Open Source / Free

• OpenStack, CloudStack (http://www.cloud.com)
• Xen Cloud Platform (http://xen.org/products/cloudxen.html)