Most played cards in 4c Aggro:

5 Decks
Mishra's Factory
18 copies - 3.6 average
Serendib Efreet
16 copies - 3.2 average
Tropical Island
15 copies - 3 average
City of Brass
15 copies - 3 average
Lightning Bolt
12 copies - 2.4 average
Disenchant
12 copies - 2.4 average
Red Elemental Blast
12 copies - 2.4 average
Swords to Plowshares
12 copies - 2.4 average
Tundra
10 copies - 2 average
Volcanic Island
9 copies - 1.8 average
Taiga
8 copies - 1.6 average
Chain Lightning
8 copies - 1.6 average
Kird Ape
8 copies - 1.6 average
Psionic Blast
8 copies - 1.6 average
Fireball
8 copies - 1.6 average
Su-Chi
8 copies - 1.6 average
Erhnam Djinn
7 copies - 1.4 average
Serra Angel
6 copies - 1.2 average
Birds of Paradise
6 copies - 1.2 average
Control Magic
5 copies - 1 average