In looking through Trainer cards for the Diglett or Pidgey Cameo thread, I found some unique cameos (forgive me if any of these have already been mentioned):
Zoroark in Trick Coin:
Charizard Mouth in The Masked Royal:
Kabutops and Persian?/Eevelution?/??? in Roxanne:
Tyrantum, Bastiodon, & Aerodactyl in the full art:
Onix on the Shirt:
But my favorite is this appearance of Dunsparce:
