The orchestras cited so far, although superb, aren't worth much when it
comes to Baroque music.  So, here's another list to cover further bases:

Amsterdam Baroque Orchestra
Boston Baroque
Concentus Musicus Wien
Il Giardino Armonico
Bach Collegium Japan
Musica Antiqua Koln
Le Concert de Nations
English Concert
Freiburg Baroque Orchestra
English Baroque Soloists

As an aside, could someone explain to me the huge appeal that the
classical music audience has for orchestral music? I've never been able to
figure that one out.  Classical music would be a significantly less costly
proposition if those large orchestras and halls didn't have to be paid for.
Example:  take Mahler's Symphony of a Thousand and knock off two zeros.

Don Satz
Efficiency Trainee