Found a list, not sure if they've all been mentioned before:
Where to find them in Disneyland Paris Park
The Park gate under the Disneyland Hotel contains numerous Hidden Mickeys.
On the glass mural at the Main Street Railroad Station, take a close look at the castle.
On the gas lamps in the Liberty Arcade and Discovery Arcade.
Cinderella's coach in the Main Street Electrical Parade, the pumpkin and wheels (upside down).
Tiles on the roof of Le Chateau de la Belle au Bois Dormant.
Lights at the rear entrance to Le Chateau de la Belle au Bois Dormant.
In Phantom Manor, look up at the ceiling in the foyer.
In Phantom Manor, on the table in the ballroom scene, look at one of the arrangements of plates.
Pirates of the Caribbean, look out for a crane holding three barrels.
On Pirates of the Caribbean, towards the end of the ride you'll see a pile of treasure, with three plates on top forming a Hidden Mickey.
In the Big Thunder Mountain loading area, on the wall clock.
On the outside of "It's a Small World", on the golden panel next to the clock.
On the castle at Alice's Curious Labyrinth.
Where to find them in Disneyland Paris Park
The Park gate under the Disneyland Hotel contains numerous Hidden Mickeys.
On the glass mural at the Main Street Railroad Station, take a close look at the castle.
On the gas lamps in the Liberty Arcade and Discovery Arcade.
Cinderella's coach in the Main Street Electrical Parade, the pumpkin and wheels (upside down).
Tiles on the roof of Le Chateau de la Belle au Bois Dormant.
Lights at the rear entrance to Le Chateau de la Belle au Bois Dormant.
In Phantom Manor, look up at the ceiling in the foyer.
In Phantom Manor, on the table in the ballroom scene, look at one of the arrangements of plates.
Pirates of the Caribbean, look out for a crane holding three barrels.
On Pirates of the Caribbean, towards the end of the ride you'll see a pile of treasure, with three plates on top forming a Hidden Mickey.
In the Big Thunder Mountain loading area, on the wall clock.
On the outside of "It's a Small World", on the golden panel next to the clock.
On the castle at Alice's Curious Labyrinth.
