The École normale supérieure is arguably the most prestigious French grande école, whose main campus is located around the rue d'Ulm (Ulm Street) in the 5th arrondissement of Paris.

(see wikipedia for more)

prestigious alumni can be found on the wikipedia article, just cite some of them:

• Claude Cohen-Tannoudji (1953)
• Pierre-Gilles de Gennes (1951)
• Jacques Hadamard
• Henri Lebesgue
• Emile Borel (1889)
• Laurent Schwartz (1934)
• René Thom (1943)