del.icio.us tipped me off to this Flash puzzle called Gridlock. It's one of those deceptively simple games that draws you in with increasingly difficult levels. No doubt, it's been gridlocking productivity everywhere.
For those who prefer something less mentally taxing, there's Fly Guy. You're just a guy in a suit, waiting for the bus, but you can fly around and do stuff. Just because. (Thanks to my friend Eric for the link.)