Try PopCap Games' 2D Game Framework (Score 2, Informative)

Check out our 2D game framework and real game samples, available at http://developer.popcap.com/index.php. We've used and continue to use this framework for all our own games. Nearly all the hard technical issues you'd need to tackle have been solved here, so you can really put your focus on game design. There's a pretty active community of people on the Popcap Developer Forums who can help you out too. Best of all, it comes with one of the most free and open open-source licenses out there. Give it a shot!