Bach's Mass in B Minor: Four lectures and an interactive manuscript (which starts playing automatically) tied to the lectures.
If you want to read about the history, construction, sounds and playing techniques of, say, the tympani, or any other instruments of the classical symphonic orchestra, Vienna Symphonic Library's Instruments Online pages are good reading and a handy resource for orchestrators.
A corpus analysis of rock harmony [PDF] - The analyses were encoded using a recursive notation, similar to a context-free grammar, allowing repeating sections to be encoded succinctly. The aggregate data was then subjected to a variety of statistical analyses. We examined the frequency of different chords and chord transitions ... Other results concern the frequency of different root motions, patterns of co-occurrence between chords, and changes in harmonic practice across time. More information, analysis, and explanation here.
The OEIS Movie is simply a slideshow of one thousand plots from the Online Encyclopedia of Integer Sequences, at two plots per second with sequence-generated music. [more inside]
If you have some time that needs to be filled with music, you might want to listen to all the symphonies of Shostakovich and perhaps all of Bruckner's as well - Bernard Haitink's recordings of these two cycles are available for listening on myspace (of all places).
The Schoenberg Code is a serial novel in 12 chapters, a parody of Dan Brown’s novel, “The Da Vinci Code,” as retold from a musical perspective by Dick Strawser. And there is much more enjoyable musical reading on his blog, Thoughts on a Train. For example, this three-part article on the strange story of Alban Berg's opera Lulu.
Imagine this: 'This evening we are going to hear the 2nd Symphony by Claude Debussy, the Austrian première of Insect Life by the Finnish opera composer Kalevi Aho, and the 2nd Symphony by Bela Bartók.’ What is a symphony? What does the concept mean nowadays? And what does it mean, to compose symphonically?
A Practical Guide to Musical Composition and Principles of Counterpoint - texts by composer Alan Belkin (quite a bit more to be found on his site).
Tubular Bells, arranged for Commodore 64: Part 1, Part 2. (Tubular Bells for the Sinclair ZX Spectrum has been on MeFi previously, but this has far more ring modulation.)
Course materials and taped lectures (nearly 70 hours worth) from John Ronsheim's classes on 20th century music at Antioch College.
Two 20th century additions to the comparatively small body of concertos for double bass and orchestra: Einojuhani Rautavaara's Angel Of Dusk (II, III), from 1980, and the 1948 concerto of Eduard Tubin (II, III). Those are courtesy of YouTube, but if you're not sated you can hear still more from bassist Phillip Serna, and a great deal more, from the fine Contrabass Conversations podcast.
You'll rarely see it staged, so might as well enjoy Bartók's lone opera, Duke Bluebeard's Castle in a beautifully filmed version on YouTube. Libretto in Hungarian, English. And a little introduction and analysis, with a particular eye toward the cryptic prologue.
Playing with Dictators - an editorial on the New York Philharmonic's decision to play a concert in North Korea. One musician's account of the performance.
Here we have a virulent earworm (with a high language-independent sing-along quotient) from early 80's Hungary. Over here we have a site for constructing catastrophic webcam karaoke versions.
Perhaps you were looking for some trance-y didjeridoo/jews harp/beatbox music today. If so, you're in luck.
Interesting discussion on classical and pop music, and two related older articles on the Pulitzer nomination process from Greg Sandow.
Orpheus and Eurydice, the acid-tinged, animated music video version.
The six string quartets of Béla Bartók: A guide for performers and listeners, by the Emerson Quartet...
The virtual flute - courtesy of the music acoustics group at University of New South Wales. If exploring the fourth octave or pondering multiphonic possibilities isn't for you, you may still enjoy a wander through the long and technical history of the instrument.
TVFolk is a collection of 400-odd videos of traditional music from nothern Europe, including a live (leek-free) performance from Loituma (below) in 2001. Other standouts include Hedningarna, JPP, and Garmarna.
Austria's AEIOU has bar-by-bar analyses of major classical works (of composers associated with Austria): audio, annotations, scores, and performance/score animations in various video formats, together with biographical essays on the composers. Some possible points of departure: 1, 2, 3.
Bad acoustic cover songs with a French accent.
Art of the States - American composers and their music. Real Audio streams of complete works.
Rondo Alla Iron Maiden (Program Notes, mp3s). As the name suggests, this new work for string quartet is a classical rondo in the style of the British heavy metal band Iron Maiden. Composer Kurt Mortensen might rather you pay more attention to some of his other works, like this charming folk-tinged trio, but I had to go straight for the silly stuff.
Arnold Schönberg Web Radio - a rotating program of documentaries, lectures, history, the composer's own words, and recordings of nearly all his works. The Schönberg center also has some beautiful manuscript pages scanned.
Several dozen folk, popular and art songs from Hungary (in Real Audio and MP3).
The Unheard Beethoven - This website endeavors to make all of Beethoven's unrecorded music readily accessible to the public. These never-before-heard works are now available to anyone with a computer, a modem and a soundcard, in the form of MIDI files. At present, over twelve hours of Beethoven's music is available on this website and in no other listenable format.