The dog from Duck Hunt is one of the oldest and best in the business. Dogmeat from Fallout 3 is a menacing force. The dog in Fable II was a bigger part of the game than I thought he'd be. Yamato from Shadow Dancer: The Legend of Shinobi had special ninja-dog training. It's kind of crazy how many courageous canines have graced videogames.
Who are some of your favorite videogame dogs? (And no, Amaterasu from Okami doesn't count. She's a Shinto sun goddess!)