I just had to brag a little bit - I made a Cookie Monster cake for Max's birthday this summer (again, I re-found it recently).
I used a round bowl as the "pan" for the head and a sheet pan for the body. I arranged it all on a cookie sheet, cut the shoulders down, made a slit for the mouth, and frosted accordingly. Instead of buying black frosting for the mouth and eyes, I used chocolate sprinkles. Add a cookie in the mouth, and viola!
Not bad for a last minute assembly (that morning!).