The remaining teams/ball parks I have not seen at all…

American League
-Oakland

National League
-Philadelphia
-Atlanta
-Cincinnati
-Denver

Add the ones I did not see a game at but seen the stadium in some form (inside or out):

American League
-Anaheim Angels (walked around stadium)

National League
-New York Mets (rained out at Shea)
-Chicago Cubs (walked around stadium)
-San Francisco Giants (ballpark tour)

Add the ones with the new ball park i have not seen

-Marlins Park (was at dolphin Stadium)
-Petco Park (was at Jack Murphy Stadium)
-New Yankee Stadium (was at old Yankee Stadium)

And my favourate ex home team that is no more...
Montreal Expos (Olympic Stadium)