Galcon
Galcon, a turn-based strategy game, takes some of the game play aspects of Pandemic and blasts them into space. Players take control over a cluster of planets and try to capture new territory while defending their existing planets from computerized attackers. Gameplay moves quickly, meaning a game can be finished in a matter of minutes instead of the lengthier Pandemic campaigns. Endless random starting scenarios ensure Galcon has some life to it. The game costs $2.99 in Apple's App Store.
Risk: The Official Game
Think of Risk as a more advanced version of Pandemic, just absent, well, a pandemic. Viruses are replaced with armies in this turn-based strategy game, with the goal of capturing territories and eventually reigning supreme as global leader. Based on the classic board game, Risk is ported well to the iPod, with multiplayer functionality that lets you pit your teeming hordes against those of your friends. Risk is available for $4.99 in Apple's App Store.
Infect Them All
Though it lacks the global bent of Pandemic, Infect Them All is a game that might satisfy your need to destroy humanity. Players take on the role of a zombie with the simple goal of infecting all the human characters on screen. As players progress through the game, upgrades become available to better help you capture (and infect) humanity. The game is available in Apple's App Store for $1.99, and includes tools to let you share and compare your best scores with your friends.