I need to find the best colon/gi surgeon in the US.  (Best as far as
most experienced, knowledgable, associated with best hospital, etc). 
This is for what we've been told will be a very complicated surgery on
my sister, in whom about a foot and a half of the colon is very
diseased with severe diverticulitis and several unkown masses that
need to be removed.  She has been hospitalized twice with severe
infections in this area of the colon and is in need of surgery asap. 
She is only 34 and has been otherwise healthy (5'10" approx 145lbs,
has 2 year old child) We are in New York but want to find the best
possible surgeon for this.

One of the most highly-regarded facilities in the United States for
colorectal surgeries is the Cleveland Clinic:

http://www.clevelandclinic.org/colorectal/default.htm

Several years ago, when a complicated gastrointestinal procedure could
not be performed by my local surgical team, I was sent to the
Cleveland Clinic for evaluation and surgery. Like most very large
hospital complexes, the Cleveland Clinic doesn't offer much in the
"bedside manner" department (you get passed from test to test and
physician to physician as if you're on an assembly line), but I found
the technical knowledge and surgical competence of the surgeons to be
most impressive.

For possible alternatives to surgery, your sister might want to
investigate naturopathic means to healing.  The work of doctor Richard
Schulze might be of interest:

Healing Colon Disease Naturally
http://www.800herbdoc.com/nhpbooks.asp

Be sure to consult with a doctor before embarking on any possible alternatives.