http://www.sfmoma.org/exhibitions/384
The thing I admire the most about Richard Avedon's portraits is how he captured everyone, celebrity or not, with such simplicity and stunning beauty! Here's one of my favorites:

The Fab Four: John, Paul, George, and Ringo.
Also memorable is Avedon's series "In the American West":
http://www.richardavedon.com/#s=18&a=0&mi=2&pt=1&pi=10000&p=7&at=0
My favorite the portrait of "Juan Patricio Lobato" (image #19 of 26); which I should have taken a photo of, but didn't cos the gallery was a little crowded at the time.
This is by far one of the best photo exhibits that I've ever seen, and one of the few that I'm planning to go see again!
I also got to finally see the new rooftop garden at the MoMA (pictured below).

Also, slightly off topic, I noticed this window display at the Marc by Marc Jacobs store (at the corner of Fillmore and Sacramento) yesterday, and was highly amused by it.

Anyway, be sure to check out the Richard Avedon exhibit at SFMoMA (now through 11.29.09)!