Angrybeth likes Psi-Ops
A game that really opened up my eyes to the crazy things you could do with the Havok physics engine was Psi-Ops:The Mindgate Conspiracy by Midway Games - made in 2004.
Though other games were already employing physics successfully to create real world simulation - it was the conceit of the player having telekinesis that created a really fun Havok sandbox. From being able to toss and whip objects and other characters around to TK surfing (standing on a box whilst picking it up with Telekinesis) created a multitude of creative ways you could complete a level.
It was through playing a session of Psi-Ops, that I was inspired to create Super-Collider.
Super-collider works through making objects in Second Life grabbable - in the edit object tabs its a tick box called Allow Others to Move. Combined with physics enabled ( and in this case - a script that makes the object behave like there is no gravity ), users can push or pull the object around in the 3Dspace with their mouse. Collision with the walls or other objects trigger notes to play.