Believe it or not, my nine year old came up with this idea for a Jon Stewart costume.
For the TV we used a shipping card board (an apple computer box, since it was sturdier). We covered it in silver duct tape and attached the Comedy Central logo and the logo for the Daily Show. A handle was taped to the bottom of the TV so he could hold it.
My son wore a suit and a tie that we had left over from a holiday, and he sprayed his hair dark and slicked it back with gel. We tried a little silver spray for the gray, but it was hard to see.
He was a huge hit at school, with both the students and parents. And he won Most Original Costume!
Very easy, and if you already have a suit and tie, it only cost a couple of dollars for the duct tape and the can of colored hair spray!