Old England. I know it sounds strange to visit a store with that name in the capital of France. But it's home to some of the finest classic British apparel anywhere. Covers the range from casual cool to black tie. I don't know what it is about British style, but it just exudes confident class, and never seems to be trying too hard.
Charvet. The epitome of French tailoring, they're shirting is truly astounding. They make a few nice ties too. Most notable to me is their elegant use of rich color. Pay special attention to the silk robe with the bow tie. If you can ever pull that off, I'd say you're in a good situation.