The manufacturers listed here are those whose products will most typically be seen in the vintage cast iron collectibles marketplace.

Birmingham Stove & Range Co. - Birmingham, AL (1902-1990s)

Hollow ware manufacturing arm of Atlanta Stove Works
Lines include:
Red Mountain (1900s-1940s)
Century (1950s-1960s)
Pioneer (1970s)
Lady Bess (1970s-1990s)

Favorite Stove & Range Co. - Piqua, OH (1916-1935)

Brands include:
Favorite Piqua Ware
Miami (economy brand)
Puritan (for Sears Roebuck)

Griswold Manufacturing Co. - Erie, PA (1885-1957)

Brands include:
Erie (1880-1905)
Griswold's Erie (1905-1906)
Victor (economy brand)(1900s-1930s)
Griswold (1906-1957)
Iron Mountain (unmarked) (1940s)
Good Health (store brand)(1920s-1930s)
Best Made S.R. & Co. (for Sears Roebuck) (1920s)
Puritan (for Sears Roebuck) (1920s-1930s)
Merit (for Sears Roebuck) (1920s)

Lodge Manufacturing Co. - South Pittsburg, TN (1910-Present)

Brands include:
Chef's Choice
Maid of Honor (for Sears Roebuck)¹
Plantation Ware

¹There is some controversy as to whether MOH was made by Lodge.

Martin Stove & Range Co. - Florence, AL (1917-1953)

Sidney Hollow Ware Co. - Sidney, OH (1888-1897)

Vollrath Manufacturing Co. - Sheboygan, WI (1884-1960s)

Wagner Manufacturing Co. - Sidney, OH (1891-1959)

Brands include:
Wagner (1891-1930s)
Sidney (1905-1929)
Wagner Ware (1914-1959)
National (economy brand)(1914-1930s)
Long Life (store brand)(1930s)
Montgomery Ward/Wardway (1930s)

Wapak Hollow Ware Co. - Wapakoneta, OH (1903-1926)

Brands include:
Wapak
Oneta (economy brand)(1912-1926)

Other often-seen U.S. cast iron foundry cookware products:

Ahrens & Arnold - Wapakoneta, OH

Alfred Andresen & Co. - Minneapolis, MN

American Brass & Iron Co. (AB&I) - Oakland, CA

Atlanta Stove Works - Atlanta, GA

Belknap Hardware and Mfg. Co. - Louisville, KY

Chicago Hardware Foundry - Chicago, IL

Columbus Hollow Ware Co. ("The Favorite") - Columbus, OH

Crescent Foundry Co. (Ozark) - St. Louis, MO

Dixie Foundry Co. - Cleveland, TN

Excelsior Manufacturing Co. (G.F. Filley) - St. Louis, MO

Keystone Food Chopper (C.I. Co.) - Boyertown, PA

King Stove & Range Co. (preceded Martin) - Sheffield, AL

W.J. Loth Stove Co. (Loth's) - Waynesboro, VA

Marion Stove Co. - Marion, IN

O'Brien & O'Brien - Chicago, IL

Orr Painter & Co. (O.P. & Co.) - Reading, PA

Renfrow Ware - Los Angeles, CA

Russell & Erwin Manufacturing Co. (R&E) - New Britain, CT

E.C. Simmons Hardware Co. - St. Louis, MO

D.R. Sperry & Co. - Batavia, IL

Stover Manufacturing Co. - Freeport, IL

N. Waterman - Boston, MA

Western Foundry Co. (Mi-Pet) - Chicago, IL

Wrought Iron Range Co. (WIRCO) - St. Louis, MO

This list is in no way meant to be exhaustive or comprehensive, but rather those manufacturers which you are most likely to encounter in your search for collectible cast iron.