I find my list shrinking every year... so many new parks!

Current:
Wrigley Field
Miller Park
US Cellular Field
Comerica Park
Dodger Stadium
Coors Field
PNC Park
Citizens Bank Park
Fenway Park
Rogers Centre

Ex-parks:
(old) Busch Stadium
Milwaukee County Stadium
Shea Stadium
(old) Comiskey Park

Still standing, but no more baseball:
RFK Stadium
Qualcomm Stadium