The IMSLP/Petrucci music library is, in a word, amazing. This wiki contains scores and parts (parts!) for something like 600 orchestral works and operas, plus chamber music, vocal music and books.
Examples? Trumpet parts for all the Mahler symphonies; Ravel’s Daphnis & Chloe and Bolero; Strauss tone poems, including the Alpine Symphony and Sinfonia Domestica; Bruckner’s symphonies; The Arban Book, for heaven’s sake. If you’re preparing for an audition, this is the place to look.
Being a wiki, it has fun things like “Random Page.” I got a Mozart piano sonata; a Schonberg manuscript of Variations on a Recitative; an Albrechtsburger Sinfonia Concertante for orchestra; 5 short pieces for piano by Busoni; and “The Ancient Music of Ireland.”