And it gets better: you could also say "Ouah", or "Ouap".
Don't know if it's just a question of different Schools of Barking, or if it depends on the size and shape of the dog you're impersonating though.
You say "Miaou" for cats, and "Cocorico" for the French totemic poultry (yeah, the one that can sing with both feet deep in sh*t).
Trivial knowledge is fun, innit?