Amazon EC2 - Amazon Web Services offers reliable, scalable, and inexpensive cloud computing services. Free to join, pay only for what you use.
Cloud4U - A cloud-based service model that provides core computing, storage and network connectivity resources on an on-demand, pay-as-you-use basis.
Microsoft Azure - Windows Azure and SQL Azure enable you to build, host and scale applications in Microsoft datacenters.
Amazon AWS - Amazon Web Services offers reliable, scalable, and inexpensive cloud computing services. Free to join, pay only for what you use.
DigitalOcean - Simplifying cloud hosting. Deploy an SSD cloud server in 55 seconds.
MacStadium - MacStadium offer Mac colocation and dedicated server rentals plus VMware Mac Pro private cloud environments for large-scale iOS app