Manhattan Brewing Co.
Mankato Brewing Co.
Marlin White Label Beer
Marshfield Brewing Co.
Marshfield Lager
Marshfield Premium

Mathie-Ruder Brewing Co.
Maui Lager
Meister Brau
Meister Brau, Inc.

Metz Beer
Metz Brewing Co.

Michelob Beer
Mickey Finn's Brewery
Miller High Life Beer
Miller Brewing Co. 
Miller Chill
Miller Genuine Draft
Millstream Brewing Co.
Minneapolis Brewing Co.
Mitchell (Harry Mitchell) Brewing Co.
Mitchell's Premium Beer

M.K. Goetz Brewing Co.
Monarch Brewing Co.
Monarch Encore

Morlein Beer
Muehlebach Beer
Muehlebach (Geo. Muehlebach) Brewing Co.
 
National Beer
National Bohemian
The National Brewing Co.
National Premium

Ninkasi Brewing Co. updated March, 2016
North Country Brewery
Northwoods Brewpub

Oconto Brewing Co.
Oconto Premium Beer

O'Doul's
Old Crown Beer
Old Dutch Beer
Old Fashioned Lager
Old Milwaukee Beer
Old Shay Beer & Ale
Old Style Beer
Olde English "600" Malt Liquor
Oltimer Beer
Olympia Beer
Olympia Brewing Co.

Olympia Gold
Osborne Brewing (not a brewery-homebrew supply shop) updated August, 2016
Oshkosh Brewing Co.