Picked up news that Microsoft is running a competition that's loosely based around the recent Global Game Jam. Although they're being very vague about the focus: you can either port an existing game or make a new one. Only thing is that it has to be in by the 30th of March. You need to be registered with the Windows Dev Center, and publish to Windows Store or Windows Phone Store
First Prize: $10,000 USD
Second Prize: $5,000 USD
Third Prize: $3,000 USD
10 Honorable Mention Prizes: $1,000 USD each
Details here: http://www.wpdevcenteroffers.com/home/contest
I'm not a big fan of the format of this compo, but I might enter one of my old games and just port it to WP. There's no stipulation that it has to be a game used in the GGJ.