I just came across True Axis physics engine. Its really amazing and I just cant stop playing one of the demos, provided on the homepage. Just check out the
demos package here http://trueaxis.com/downloads.html and try "Cars". Its freakin' addictive.

Funny

looks interesting

Nice, but not quite perfect.

Vain

Yep the cars one and the fast moving object were quite fun!

The box stacking is actually rather impressive. It's amazingly stable. I've been implementing a similar physics sandbox using ODE, and I can't get anything like those towers to stand upright. It usually just collapses in on itself after a while. (The bottom boxes slip out from underneath the stack like bars of soap.)

I dont think ODE is good physics engine. After watching demos I consider Newton Dynamics much more reliable engine, however the defaoult cars behaviour is not very good anyway.

Quote from himself :

I dont think ODE is good physics engine.

That might very well be. I'm using it mostly because of the "Open" part to be honest. Haven't really looked around for alternatives though.