How many pitchers have thrown a no hitter twice in Mlb history?

Through the 2008 season:

7: Nolan Ryan

4: Sandy Koufax

3: Bob Feller, Cy Young, Larry Corcoran

2: Mark Buehrle, Randy Johnson, Hideo Nomo, Bob Forsch, Steve Busby, Bill Stoneman, Ken Holtzman, Don Wilson, Jim Maloney, Jim Bunning, Warren Spahn, Carl Erskine, Virgil Trucks, Allie Reynolds, Johnny Vander Meer, Dutch Leonard, Addie Joss, Frank Smith, Christy Mathewson, Ted Breitenstein, Adonis Terry, Al Atkinson, Pud Galvin