Angry Birds

From Developer:

The survival of the Angry Birds is at stake. Dish out revenge on the green pigs who stole the Birds eggs. Use the unique destructive powers of the Angry Birds to lay waste to the pigs fortified castles.
Angry Birds features hours of gameplay, challenging physics-based castle demolition, and lots of replay value. Each of the 63 levels requires logic, skill, and brute force to crush the enemy.
Protect wildlife, or play Angry Birds!
Video made by Kombo (www.kombo.fi)

They have lite version of the apps which is free .  And if you're not satisfied buy the full version :-p

I suggest you watch their video first before playing cos it's the story of the game.  The video is funny.  The game is funny too.  I find it enjoyable, entertaining and addicting.  You must have strategies to unlock each level.  A nice game for kids too.  When my son first played the game, he keeps on laughing hi hi.

A must have apps in iPhone.

My iPhone screenshots: