Most played cards in Shops:

3 Decks
Copy Artifact
12 copies - 4 average
Icy Manipulator
12 copies - 4 average
Mishra's Workshop
12 copies - 4 average
Mishra's Factory
12 copies - 4 average
Triskelion
12 copies - 4 average
Su-Chi
12 copies - 4 average
Fellwar Stone
11 copies - 3.67 average
Juggernaut
10 copies - 3.33 average
Swords to Plowshares
8 copies - 2.67 average
Scrubland
8 copies - 2.67 average
Disenchant
8 copies - 2.67 average
Tetravus
8 copies - 2.67 average
Tundra
8 copies - 2.67 average
Underground Sea
8 copies - 2.67 average
Control Magic
7 copies - 2.33 average
Blue Elemental Blast
6 copies - 2 average
Clay Statue
6 copies - 2 average
Animate Dead
5 copies - 1.67 average
Counterspell
4 copies - 1.33 average
Mana Vault
4 copies - 1.33 average