"Saw this on the telly last night, on one of those programs that show adverts from other countries.
"A dalmatian print pillow cover is left on a clothes line outside to dry. The wind blows it off and it lands across a small rocking horse. A nearby dalmatian sees it and starts humping it for a minute or so. Cut to scene of a man restlessly nuzzling his pillow at night, with the audience going Eeew. ;)" [Thanks Locandez]
Alpo Complete (1999)
"Sam" is an intact male Dalmatian, though I couldn't be sure until I freeze-framed when he was silhouetted in front of a fire truck's chrome hubcaps.
GiardiaVax (1999)
"Bo" is an intact male (mixed breed?) dog; he holds a teddy bear in his mouth and sits facing the camera; his sheath opening is pointing directly at the camera.
Lycos
To advertise the Internet search engine, they use a (probably neutered) male black lab (named Lycos?) to fetch things. When "Lycos" is told to fetch Claudia Schiffer, he's shown briefly from the rear, and his anus is clearly visible (though dark).
Also, according to "SH," in that same ad, Lycos seems to be "sporting an erection.... Watch the bottom of the screen, about 1/2 way thorugh, right before the dog fetches a car."
Maytag
The Maytag repairman's dog is a female basset hound [Thanks MZ]
Miller Beer
The gender of the dog in the "man dances with dog to get beer" commercial is male. The editing of the commercial clearly indicates that they deliberatly avoided any shots of the dog's crotch. The dog also didn't have any nipples, another male trait. Since female Danes are shorter than the males, they had to use a male Dane to match the height of the actor. [Thanks MZ]
Red Dog Beer
The bulldog walking around in the ads is always a very intact male bulldog. (These commercials have not been shown for a while. [Thanks MZ]
Taco Bell
The Chiahuahua is female [Thanks MZ]
Volkswagen
In the commercial where the panting dog is sitting in front of the fan, he appears to have an erection, but the picture is too dark to see it. [Thanks MZ]