This is a jam piece that my brother and I had done for our sketch-drive. My brother drew the Grey Gargoyle, I drew Thor. This was done in less than two hours, and the only thing difficult about it is figuring out a good pose to put the characters in, knowing that its a jam piece.
I'm pretty satisfied with how it turned out. I was also surprised that the buyer preferred to keep the piece in black & white, considering how much he had donated.
We're still accepting donations for sketches, see this entry for more details.