WorkSpaces by Amazon only delivers the Windows 7 Experience via Windows Server 2008 R2. As a result of Microsoft's SPLA, no other licensing is needed. Amazon also offers Active Directory integration.
Several pricing tiers are available ranging from $35 per month to $75 per month depending on hardware and software options with no order minimum. WorkSpaces is based on a heavily modified version of the open-source Xen hypervisor, providing only persistent desktops, and utilizing the PCoIP protocol.