From Joystiq. Patrick Curry is a video game designer, and for every week of this year he’s posting an idea for a game—and they’re excellent, inventive, and well-thought-out (considering they’re weekly). Rather than summarising them here, I’ll just suggest you take a look at them yourself.
One of my favourites is the Blackout concept:
Blackout is a survival game with a realistic premise: you’re trapped in a large urban city that’s completely devoid of electricity. There aren’t monsters, zombies, or aliens taking over the city… just other people. How will you escape? How will you survive?