Baseball For All is a wonderful, impactful organization founded by Justine Siegal that is dedicated to keeping more girls in the game. For a map of teams, click here.
MLB puts a number of programs together every year. For younger girls, they have Trailblazers. MLB also offers the Elite Development Invitational and MLB Grit. Grit serves as somewhat of a feeder for the US women’s national team (selection process info is here). MLB also offers the Breakthrough Series for the older girls.
Women’s baseball tournament every year In Virginia: http://www.easternwomensbaseball.org/diamond-classic-support/
The Boston Slammers have a number of girls teams at a variety of age groups and also have a great network of people to help keep girls in the game.