An immense materpiece of a youthful Corot: Le pont de Narni (1926). Actually my personal favorite.
Breathtaking how he captures the reflection of the sunlight on the water!
La femme à la Perle (1869), arguably his best known work:
Imho, a work that can easily compete with La Gioconda.
Souvenir de Mortefontaine (1864).
You can admire it in the Louvre, which has had it since 1889.