I wouldn't say AWS is the only option, probably just the most popular one. Other options might be Rackspace, Windows Azure (I think you can run Linux VMs, howe

I wouldn't say AWS is the only option, probably just the most popular one. Other options might be Rackspace, Windows Azure (I think you can run Linux VMs, however I dont know how well that's working) or Google Compute Engine (rather new, so YMMV). Those are probably the biggest players in the cloud market.