Most played cards in 8 Cast:

6 Decks
Thought Monitor
24 copies - 4 average
Darksteel Citadel
24 copies - 4 average
Memnite
24 copies - 4 average
Urza's Saga
24 copies - 4 average
Thoughtcast
22 copies - 3.67 average
Springleaf Drum
22 copies - 3.67 average
Metallic Rebuke
20 copies - 3.33 average
Frogmite
16 copies - 2.67 average
Ornithopter
16 copies - 2.67 average
Cranial Plating
16 copies - 2.67 average
Sojourner's Companion
16 copies - 2.67 average
Razortide Bridge
12 copies - 2 average
Mistvault Bridge
12 copies - 2 average
Treasure Vault
10 copies - 1.67 average
Damping Sphere
10 copies - 1.67 average
Dispatch
9 copies - 1.5 average
Tormod's Crypt
9 copies - 1.5 average
Relic of Progenitus
9 copies - 1.5 average
Seachrome Coast
8 copies - 1.33 average
Ingenious Smith
8 copies - 1.33 average