Monaco is an indie co-op stealth game that has been in development for a couple of years, got some high IGF praise, and is finally coming out of the shadows for the public's entertainment. The composer who provided music for fl0w and Journey also pitched in for this game. The game will be available for PC (Steam and non-Steam flavors), Mac, and XBLA. In addition to the RPS tag for the game, here are a few videos to whet your appetite:
100% speedrun of a level from closed beta, very recent [spoiler, of course]
Teaser trailer announcing XBLA availability, two months ago
Gamespot coverage, about half a year ago
Narrated walkthrough by devs, almost a year ago
Additional information and possible spoilers at the Monaco Hideout wiki.