This weekend is the classic monolith of game jams, Ludum Dare #25! Theme is still pending for a few more hours...
Also, this weekend in New York City is a special game jam hosted at Parsons called "Game On", co-sponsored by Github and Mozilla. The main requirement is to make an HTML5 game. Prizes include a trip to GDC 2013 (wow!) and I think there's free food to jam with, at least. (And as long as you're here this weekend, also check out Spacewar! at the Museum of the Moving Image, charting the long lineage of shooters from ur-game "Spacewar!" on a PDP-1 replica through Metroid II and ending with Halo 4.)
ALSO, this month in Chicago, there's the Six Pack Jam. Jake Elliott and friends are putting an arcade cabinet in some bar in Wicker Park and they want cool games to put on the cabinet! Here, the implied constraints are 2 player compatible modes with short arcade-scope play sessions, but maybe that's just my interpretation.
You could, potentially, make a 2 player HTML5 game with [LD theme] and submit everywhere. Whoaa.