I think people who read RPS will be interested in what I've launched: Nimble Servers - the first company to offer game servers on demand at hourly rates!
Servers start from just £0.06 an hour for Team Fortress 2, Counter-Strike: Source and 1.6. We also have Minecraft at three different price points. All the servers are currently in the UK, but we will be adding more locations and games as fast as we can. You get full FTP access and when you shut down servers we save all your changes and restore them automatically the next time you come back.
This clearly isn't meant to be a replacement for large servers that run 24/7, but there is no arguing against the fact that a lot of servers are sitting around empty most of the time! We feel we are the perfect solution for groups of friends, clans and people who want to run servers for a variety of games.
Feedback, game suggestions, criticism and puns welcome. If you make an account on the site post here with your username or email me (firstname.lastname@example.org) and I'll sort you out with some free credit :)
Added support for Left4Dead2! Also added referral system with generous 20% bonus.