To the people trashing Harper because of his .220 batting average, he's still one of the better hitters in the game. He's having a bad year, but obviously he's a MASSIVE upgrade over what we currently have in CF/RF.
Plus, his bad year up to this point doesn't necessarily mean he will continue to play at the same level. I think his strikeouts will stay high, but we'll see his batting average rise, as his BABIP (.241) has been pretty bad this year compared to his career (.315) and the league average (around .300).
I wouldn't give up McKenzie, Bieber, Nolan... but I'd probably do something around Chang or, preferably, Benson.