Ooh! Darkseid/Galactus: The Hunger! That was the sweetest idea for a crossover. It was fan inspired too, a guy asked if they had ever considered it at a con and the response was something like "Well we will now!".
I enjoyed superman/silver surfer, but superman/fantasic four now that i think about it was a lot better than jla/avengers. No doubt one of the top ten crossovers. Also, just a quick question: does anyone think think green lantern/silver surfer was worth $40 cause thats what i paid for it