Juilliard's Manuscript Collection website (flash, music) generously makes available to the Internets a boatload of score manuscripts. Mozart, Ludwig Van, Brahms, it like nev4r ends! (via Alex Ross)
A quick note to the Juilliard designer team: brevity is awesome but if you need to shorten "Figaro" use a different combination of letters, because as it is on your website now (see below), "Moza" for "Mozart" is cool, but "Figaro" became a very widely used crude, four-letter Italian anatomical term (that would have amused that h0rndog Da Ponte a lot, but still...)