Link to the app found at: http://itunes.apple.com/us/app/plants-vs-zombies/id350642635?mt=8
This application is a wonderful cannon defense/strategy game where you build flowers to combat the evil zombies trying to break into your farm house. It has very simplistic yet satisfying graphics and many variations in game play.
The initial levels are very simple, but as you keep going, more complex enemies appear and you also unlock more complex and condition specific flower turrets to defend against them.
At $2.99 US I would highly recommend this game because you will get many many hours of entertainment out of this very addictive app.