Debussy's 24 Préludes, orchestrated by Colin Matthews; Tchaikovsky's Mozartiana (orchestrations of Mozart piano pieces); Mahler's Des Knaben Wunderhorn, orchestrated by Harold Byrns (friend of Alma Mahler); Schubert Lieder orchestrated by Britten, Brahms, Reger, Berlioz, Liszt, Webern and Offenbach; Weber's Invitation to the Dance orchestrated by Berlioz. Brahms's Variations and Fugue on a Theme by Handel, orchestrated by Edmund Rubbra; Satie orchestrated by Debussy and Poulenc; Schubert's Wanderer Fantasy arranged for piano and orchestra by Liszt; Schumann's Fantasy in C major orchestrated by Hans Zender; Grieg's Lyric Pieces orchestrated by the composer; string orchestra arrangement of Beethoven's late quartets; and many other curiosities.
Here's the Spotify playlist: Orchestration As Adaptation (209 tracks, total time: 18 hours). Press Ctrl (CMD)+G to browse in album view. Recommendations are welcome.
Did I forget something? Oh yes, Pictures At An Exhibition, orchestrated by master colourist Ravel.