Microsoft is offering a great incentive for Global Game Jam teams at UMBC who make a Windows Phone game this weekend: a Windows Phone. Come early Friday (at 4pm) to UMBC ENG 005 to see a pre-jam demo on developing Windows Phone games. There will be a Microsoft representative on site this weekend to help you out if you have problems, and any team that makes a Windows Phone game gets a free phone!
Or sign up online and come at 5pm for any of the other ways of developing game jam games: Microsoft XNA Game Studio, Flash, Unity (free Pro trial available for game jammers), GameMaker (free HTML 5 version for game jammers), or any other freely available game development tools.