Recently I was reading about Arscoins and the usage they made of the free Amazon EC micro instances. Intrigues I decided to take a look.
Amazon have a free tier of services. Minimal devices with enough hours to run all month. I chose an Ubuntu Linux instance and after running through a simple sign up had an instance ready to go. Using shared keys I could ssh to it (the only way to go) and I had set firewall rules so that only a couple of static addresses could get to it. Amazing! It was all up and going in about 15 minutes. Only a barebones server of course but enough for testing and the obligatory oooh from my co-workers.
The instance is free for 12 months and I've set alarms so that in the case of exceeding usage I will be notified of any billing. They also offer Windows servers too and a variety of different operating systems. For the minimal amount of time involved it was a great experience. I strongly recommend treating the instance like a server and keeping it updated and secured.