Holst - Suite No.1 in E-Flat Op. 28 No.1 (for wind band)
Holst - The Planets
Orff - Carmina Burana
Vaughn Williams - Lark Ascending
Ravel - Bolero
Ravel - Daphnes Et Chole Part II (with choir)
Gilbert & Sullivan - Mikado
Beethoven - Violin Concerto
Dvorak - New World Symphony
Gershwin - Rhapsody in Blue
Grieg - Piano Concerto
Strauss - Blue Danube

I tried to not think of songs I hear in movies, but in the case of Blue Danube I couldn't help it. I wonder what it must be like to not have that song connected with 2001.

I've returned to my list of 250 songs for the AM Forum back in 2005 and these are my favourite classical SONGS (well, really pieces of music part of a bigger classical work):
1. SERGEY PROKOFIEV “Romeo and Juliet, Suite No. 2 for orchestra, No. 1 Montagues and Capulets” (1936).
2. JOHANN SEBASTIAN BACH “Matthäuspassion (St. Matthew Passion), No. 1 Chorus: Kommt, ihr Tochter, helft mir Klagen” (1736).
3. ANTONIO VIVALDI “Violin Concerto for violin, strings and continuo in G minor, ‘L’estate’ The Four Seasons ‘Il cimento, No 2’, 3rd Movement: Presto” (1725).
4. ERIK SATIE “Gymnopédies No. 1” (1888).
5. LUDWIG VAN BEETHOVEN “Symphony No. 3 in E flat major ‘Eroica’, 2nd Movement: Marcia funebre, Adagio assai” (1803).

And I will add some movie soundtrack pieces (style in which one can find real masterpieces):
1. HENRY MANCINI “Moon River” (1961), the version sung by Audrey Hepburn in her window sill is a prodigy of delicacy.
2. NINO ROTA “Godfather Waltz” (1972), a lonely trumpet and the face of Marlon Brando emerging slowly from the dark.
3. JUDY GARLAND “Over the Rainbow” (1939), now it seems that is a gay anthem, but in my ears it always will be related with the absolute happiness only possible in childhood.
4. LEONARD BERNSTEIN “Somewhere” (1957), there’s a place for us / a time and place for us / hold my hand and I'll take you there / somehow / some day / somewhere.
5. JOHN WILLIAMS “Theme from Schlinder’s List” (1993), probably the saddest melody ever.
6. STANLEY MYERS “Cavatina – Theme from the Deer Hunter” (1979), beautiful moody piece for classical guitar.

"Lick My Love Pump" By Nigel Tufnel of Spinal Tap.

(He's very much influenced by Motzart and Bach, so it's kind of a "Mach" piece, really.)

Totally forgot about that one! Good call.