Derek Yu's jawdropping Spelunky, a mechanical mashup of Nethack with a 2D platformer, has finally hit version 1.0 and is celebrating with a real homepage (its homepage before now was a forum thread somewhere), and the news that it will show up on Xbox Live Arcade in 2010. Congratulations on your excellent work, Derek, and props to Microsoft for picking a winner, too!
The game runs on Windows, and, sadly, doesn't work under emulation on a Mac, at least not my MacBook running VMWare; it needs special graphics-card voodoo that doesn't pass through. But if you can run Windows natively, you really should give this game a spin. Or 20 spins. (It's short and you die a lot, but I guarantee you'll die in a new and thoroughly entertaining way each time.)