Lego? Pff...
Fischer Technik is king. Then meccano. Then lego.
That is all.
Deleted
I've seen a lot of fancy stuff in lego. It takes real talent to build a robust engineering solution with lego - anyone can do it with real industrial-strength metal parts.
Oh, and this book should be on the list, but because it's just too cool to leave out:
http://www.amazon.com/exec/obidos/ASIN/1593271379/bookstorenow16-20