Always a very fun topic. I hadn't thought about my own list in a long time, so I took yours and edited it. There's a fair amount of overlap with yours. I did include defunct parks because it's a pretty substantial list which proves just how old I am. Have a great time in DC, Jere.

Major league parks I've seen a game in:

Fenway Park
Shea Stadium
Yankee Stadium I (Sept. ’73)
Yankee Stadium II
Yankee Stadium III
Memorial Stadium (Baltimore)
Camden Yards
Tiger Stadium
Comiskey Park I
Comiskey Park II
Dodger Stadium
Anaheim Stadium
Candlestick Park
Oakland Coliseum (Game 1 ’89 WS)
Pac Bell (or whatever they call it now)
Kingdome
Metrodome
County Stadium (Milwaukee)
Miller Park
Municipal Stadium (Cleveland)
Jacobs Field
Veterans Stadium
Citizens Bank Park
Olympic Stadium (Montreal)
Wrigley Field
Three Rivers Stadium
PNC Park
Busch Stadium I
Busch Stadium II
Chase Field
RFK Stadium (exhibition game)
*also saw several major league exhibition games at Doubleday Field

Parks I've been on the outside of:

Safeco Field
Riverfront Stadium (while under demolition)
Forbes Field (what remains on the Pitt campus)
Comerica Park (while under construction)
Skydome (or whatever they call it now)
 

Nice. I actually did include defunct stadiums, but said I didn't...I guess I was thinking of Braves Field in Boston, as an example of a field that has parts still standing that I've been "to," but I never saw a game there when it was still a working stadium.
 

Oops...I haven't been to the new YS yet; I thought I had deleted that one when editing your list. M-m-m-m-y-y-y mistake. And since I've been to the Mall of America, that means I've been to the site of Metropolitan Stadium in Minnesota too. But my list looks ok otherwise. I'll probably get to the two new NY parks this year; also would like to make it to DC and KC.
 

Oh, and I drove past Tropicana Field years before the Devil Rays even existed, but that place shouldn't even count as a ballpark.