Won't surprise me if the Q6600 goes up in price a little bit. It's EOL has been announced and I think its the only 65nm quad still around in quantity. Some motherboards don't support 45nm, so for some the move to quad will require either the Q6600 or a new motherboard.
Q8200 is cheaper than the Q6600, Q8300 is the same price, and a Q9400 won't cost much more, I don't see the need for purchasing a Q6600 if your motherboard supports 45nm quads.