How about "Yes, we're hoping for a boy... or a girl. One of those two would be great!"
.............classic. Love it.

YOur going to get those comments regardless - if you had 2 boys you would get the question about the girl, if you had one of each you would get some other stupid question. As long as you have a couple of these one liners up your sleeve, you will be fine.....and proud.

ETA; i hate the look when they see you have three girls, and they look at you like youve got three little guinea pigs, or 3 ferral cats following you...'you have 3 of them ???' gawd, i hate it.....