I was able to hit up Vivienne Westwood on Melrose this past July and pick up some real nice stuff at 50%. Pure luck.
Syms. Trinity Place. Go.
And like the lady said, get it tailored. A $300 suit tailored to fit looks better than an ill fitting anything. Start with the basics-- slate grey or navy. Oh, and get some good shoes to go with it. Don't skimp there, either.