Downloadable pdf scores of entire movements and works (courtesy of the IMSLP. Note that the IMSLP also gives links to recordings on Amazon.com)
Beethoven, L. v.
Sym. No. 1, op. 21
Sym. No. 2, op. 36
Sym. No. 3, op. 55 (Eroica)
Sym. No. 4, op. 60
Sym. No. 5, op. 67
Sym. No. 6, op. 68 (Pastorale)
Sym. No. 7, op. 92
Sym. No. 8, op. 93
Sym. No. 9, op. 125
Sym. No. 9, op. 95 (“From the New World”)
Sym. No. 1 – this score is from the Archives of the New York Philharmonic, and is an amazingly vivid scan of Mahler’s own score, all 176 pages of it. As you go from page to page, the pages turn before your very eyes. The score (reproduction) size is a bit small to read the notes clearly, but you can see Mahler’s original markings in the score in blue and red pencil. What an age we live in.
For lagniappe, also on this web page are recorded samples of all the Mahler symphonies. There is also a feature (link at the bottom of the page) on Mahler when he was in New York. Thank you, NYP.
Midsummer Night’s Dream – this is a pdf download of the horn part; the famous Nocturne solo is on page 5 and 6.
Don Juan, op. 20
Tod und Verklärung, op. 24 (Death and Transfiguration)
Till Eulenspiegels Lustige Streiche, op. 28
Also Sprach Zarathustra, op. 30
Don Quixote, op. 35
Ein Heldenleben, op. 40
Eine Alpensinfonie, op. 64
Indiana University’s William and Gayle Cook Music Library offers viewing of a number of orchestral scores, including Bach Brandenburgs, Beethoven Symphonies, Berlioz Symphonie fantastique, Brahms Academic Festival Overture, Ein deutsches Requiem, 4 symphonies, Bruckner symphonies 1, 2, 3, 4, 5, 7, 9; plus others including Haydn, Liszt, Mendelssohn, Mozart – symphonies & horn concertos, Rimsky-Korsakov, Rossini, Saint-Saens, Smetana, Stravinsky, Tchaikovsky, and more.