I would like to introduce the Detroit Symphony Civic Ensembles - I'm in the Sinfona:
http://www.detroitsymphony.com/main.taf?p=4,3
it is SOOOO fun
and also Oakland Youth Orchestra - I'm in Philharmonia:
http://oyomi2.org/
OYO is better for group fun, CYE is better for section fun.
all in all, they are both fun
alex