Amazon announced the ability to run Windows virtual machines on their cloud computing platform, EC2, a few weeks ago. I had the opportunity to play with the technology for a few weeks and I was really impressed all around with the experience. If you're looking at solutions for on demand computing or want to have a relatively inexpensive and flexible hosting solution you can control completely, you should definitely take a look at EC2.
I wrote a couple of articles for Amazon as part of the launch of Windows on EC2. The articles cover deploying an ASP.Net app on an EC2 instance and configuring SQL Server 2005 to work with the Amazon EC2 platform. If you're interested in getting a quick feel for how the platform works, check these articles out: