I'm sure many on here would agree, but Legos are one of the best educational toys.
My wife's brother used to play with them a LOT. He is now a mechanical engineer.
I used to play with them quite a bit, and today I'm a computer programmer.
I will say, though -- I know other people who played with them who are merely very "creative" today. Many are unemployed, or work at unskilled jobs that anyone with a healthy/strong body can do.
But a single toy can't give you *everything*, including ambition. The fact that the toy helps develop the "building" and "creating" parts of your child's mind is sufficient to make them well worth the cost.