http://www.addictinggames.com/fantasticcontraption.html
This is an amazing game. Probably the funnest physics flash game I've ever had the pleasure to play.
It's fairly difficult, but you'll eventually learn clever tactics. I urge you all to play it, and pay the $10 for the full version (custom levels and hundreds of others).
Okami
To lavish praise upon this title, the assumption of a common plateau between player and game must be made. I won't open my unworthy mouth.