First, we have Ziggyware's "Holiday Contest" when you can win one of the three available DX10-ready gfx cards plus subscriptions to the Microsoft XNA Creators Club, just by writing an XNA-based tutorial or a handy tool to help you develop your XNA creations. Piece of cake!
Second, we have the second edition of the "Dream.Build.Play compo", which includes the "warm-up challenge". Although the main compo's "precious treasure" wasn't yet disclosed, there are great prizes ahead for those who enter the challenge: (a) the possibility of an intership at Microsoft Research, Rare Ltd. or Lionhead Studios, (b) tickets to show your entry at GDC'08, and (c) $3,000.
Third, the "InstantAction Game Developer Contest" organized by GarageGames. The task: to create -at least- a playable game demo by using whatever engine you want. The grand prize: a publishing deal with InstantAction.com plus a lincese to Unity Pro with Asset Server (valued 1,999 american dollars).
Fourth, the ImageCup's "Game Development Competition". If you're a student and love using XNA GS for your game creations -as much as I do- you may find this one is the right for you. Hesitating? Read on: "... Not only will cash prizes be awarded, these winners will then have an opportunity to come to Microsoft and present their entry to the Microsoft games management team for possible inclusion as a download in the popular Xbox LIVE Arcade service or MSN Games Web site. The first place team or individual will also win the opportunity to become an apprentice at Microsoft's Interactive Entertainment Business as part of its internship program ...".
Last but not least -hang on to something, Acclaim's "Project Top Secret". I won't comment on this one because it took my breath away, and I'm recovering, so I'll just quote the following: "The winning Indie Development team, which will develop the game, receives an instant prize of $100,000 and Acclaim will pay the license fees for whatever commercial game engine the team chooses. This combination is capped at $1,000,000. Yes, you are free to use ANY commercial game engine!".
And these are just a few compos. You may find plenty more, just do a google search to be surprised.
But which one suits you and your team? There lays the tricky part ... are you ready to face the challenge? If so, go ahead, choose your compo, and slay the dragon!