20th Century Music
I just discovered which unlike other "web radio" sites includes non-mainstream music. (Most of the "alternative" channels are in fact very mainstream.) My favorite Spinner channel is (of course) the 20th century music channel (I'm listening to it right now which catalyzed me actually launch this page).

The New Sounds program produced by WNYC is the best source of 20th century music I've ever heard. I used to listen to this John Shaeffer creation once a week for one hour in Boston until the station (WGBH?) cancelled it. On a business trip to New York I discovered that this show was not one hour per week, it was one hour per day! They have Real Audio archives as well as play lists online going back to mid-1999.

After decades of being technically unfeasible, Ballet Mecanique has finally been performed as originally written.

Here's more links to sites that carry "Jeff Music" (as my spouse and colleagues sometimes refer to it):
 Forced Exposure
 Lovely Music  (many links to new music happenings, mostly in NY City)
 Cadence (jazz oriented)

Twenty years ago, almost every Boston Symphony Orchestra performance include at least one piece from this (well really the last century). Unfortuneatly, not enough of us appreaciated this and this policy was dropped.

Folk, aka Acoustic, Music
The sleeper CD of the decade (90s) has got to be Suzi Katz's Debut Album, the site has Real Audio samples. I stumbled upon this in a cut out bin at a used CD shop and it became an instant (and persistent) favorite, I've even got a few tracks from it in my MP3 player.

Extended Techinque
Every beginning musician starts by making mistakes in technique and vows to eliminate these mistakes from their playing. Some of these musicians succeed and become very good at playing "cleanly". A few of these accomplished musicians ask the question "what other sounds can I make?", come up with some answers and integrate these sounds into very musical, though avante garde, pieces.

The funny thing is that many of the sounds produced by "extended techniques" are the very same sounds that were "mistakes" in early playing. The difference is that in the hands of a really good musician these one time mistakes can be used to produce wonderful modern musical.

Here's some of my favorites:

In Robert Dick's case, he set out on a ten year quest to catalog all the sounds the (Western, transverse) flute could make with only three restrictions,
producing the sound: The results are extensive, playing multiple notes (really overtones) at once, humming into the flute (Ian Anderson uses this technique as well), plugging the far end of the instrument with a cork. Dick does a spectacular job selecting techniques that work musically as well as interstingly in both new works and new arrangements of established works.

The Joe McPhee recording was recently re-released after a long stint as a collector's item.