Definitely the Noctua NH-U12P IMO. I have an i7 920 also and, after doing a bit of research, intend to buy this cooler as soon as I can get the money together. Make sure it is the SE1366 version you get as it comes with two fans (plus the original won't mount on the socket 1366 motherboard). Check out this review also:
http://www.legitreviews.com/article/880/1/