The Denver Museum of Nature & Science has a sweeet exhibit entitled Engineer-It! going on right now.
Fantastic stuff for kids of all ages... check out Max the Rocket Man here.
My favorite exhibit was the old volunteer dude pitchin' a new look on an old scene. He had these cool wire forms that he dipped in bubble go-go juice and created some *incredible* surface-tension bubbles.

Truly Bitchin' Bubbles!

A closer view of the straightest lines I've seen in Nature!