Two game development "competitions" popular amongst the participate in are happening in April/May. Ludumdare 48h (from scratch, solo competition using any language) and Pyweek (one week, solo or teams, using python). Both are not about prizes, but are about a creative outlet for heaps of people making games at once around the world.
Ludum Dare 20 – April 29th-May 2nd WeekendFind out more about Ludum Dare - "Ludum Dare is a regular accelerated game development Event. Participants develop games from scratch in a weekend, based on a theme suggested by community."
Find out more about PyWeek - "Invites entrants to write a game in one week from scratch either as an individual or in a team. Is intended to be challenging and fun. Will hopefully increase the public body of game tools code and expertise. Will let a lot of people actually finish a game. May inspire new projects (with ready made teams!)"