Worth a quick mention: The New York Times ran a story yesterday profiling the International Music Score Library Project, a crowdsourced web site that indexes classical music scores (though not without raising some copyright concerns along the way). IMSL hosts 85,000 scores with several thousand new ones coming online every month. You can find Bach's Brandenburg Concertos, Mozart's Eine kleine Nachtmusik, Beethoven's Symphony No. 5 – in short, the major ones along with the minor ones. And, in some cases, the archive includes audio recordings. Tchaikovsky's Nutcracker offers an example. You can find a full list of free audio recordings (arranged by composer) here.