I think it should be pointed out to non-Americans here that stadiums such as the above Giants Stadium shown with 80,000 Soccer Fans are very misleading, these are doubtless international matches or perhaps an exhibition match, or perhaps a photo from WC '94. New York would be lucky to get 15,000 on a good day. Those stadiums are outrageously bigger than the demand because they are gridiron stadiums.
The biggest Soccer Specific Stadium is the LA Galaxy one (also they have the biggest turnout and revenue in the league). Always found it weird that LA happily supports two soccer clubs from a league of twelve, but no NFL Franchise from a league of 32.