Chillingo has a ton of addictive games for both the iPod Touch and iPhone. Yesterday, it was Guerrilla Bob making a ruckus. Today, it's Leonardo da Vinci. Well, OK, not him directly, but a puzzle game inspired by the great inventor. Cogs is a one-of-a-kind puzzler that'll keep you entertained, just as long as you don't mind plunking down a few bucks for the full game.