For a comprehensive list of the most commonly requested extracts with measure numbers, and instructions on how to practice them, I recommend Orchestral Excerpts for Flute by Jeanne Baxtresser [Theodore Presser Company] and Orchestral Techniques for Flute and Piccolo: An Audition Guide and an Inside Look at Symphonic Performance Traditions by Walfrid Kujala [Progress Press].

The following is a short list of frequently asked principal flute orchestral excerpts that I encourage my students to practice and memorize:

Beethoven: Leonore Overture No.3 flute part score
Beethoven: Symphony No.3 flute part score
Bizet: Carmen - Entr'acte flute part score
Brahms: Symphony No.1 flute part score
Brahms: Symphony No.4 flute part score
Debussy: Prélude à l'après-midi d'un faune flute part score
Dvořák: Symphony No.8 flute part score
Hindemith: Symphonic Metamorphosis flute part score
Mendelssohn: A Midsummer Night's Dream flute part score article
Prokofiev: Classical Symphony flute part score article
Prokofiev: Peter and the Wolf flute part score
Ravel: Daphnis et Chloé flute part score
Rossini: William Tell Overture flute part score
Saint-Saëns: The Carnival of the Animals - Volière flute part score article
Stravinsky: Firebird Suite (1919 version) score
Strauss: Till Eulenspiegel's Merry Pranks flute part score