what is the best medium to store high quality music for the most (say
100) yrs. I am a composer/performer and I don't want my music to be
lost.

Vinyl masters-- the metal dies used to stamp "old time" records.

Storage wise, you have several options.

Magnetic Media, Optical Media, or Solid-State.

Magnetic media doesn't fair well with long term use.  Tapes, held
under perfect conditions, degrade within 30 years.  In addition, 10
years after writing them, you'll most likely not have a system that is
comptabile to read.

Optical Media such as CD and DVD can last 50-100 years if left in a
constant temperature enviroment and not exposed to sunlight.

Solid-state storage, such as Flash drives, have yet to be put to the
test, but they look promising.

Something like the above user's comment would work, but isn't the most
practical of methods.

The form of storage with the most longevity is, oddly enough, paper. 
Some companys who wish to preserve data that can be retrieved exactly
as it was written over a very long time print it out and then put it
onto microfiche.  Then store these more or less indefinitely.

For music, unfortunately, this isn't very practical either, as you
would have to record it in a lossless format and then print out the
binary code.

The best and most feasible method of storing such files for a long
term would be in a fully redundant data center.

I thought I read recently that CDs weren't nearly as long lasting as
originally thought (I am always suspicious of the longevity of
ANYTHING laminated and would run away from a house built with
engineered joists with all speed) and that CD-Rs or CD-RWs were even
worse than the older CDs.

Taishar does make a valid point with paper being an excellent medium--
it has served for Beethoven, Mozart, Bach, and thousands of others. I
suppose you mean you want your performing your music to last,
Elewhale?

One of my worst fears is that a perfect sound storage medium will be
developed and all eternity can listen to William Shatner's version of
"Rocket Man" or Sebastian Cabot's rendition of "Like a Rolling Stone."