These are the most commonly used cards in Hearthstone. Data is taken from the decks uploaded to https://hearthcard.io/
Guardian Augmerchant
In 3 Decks
Palm Reading
Insight
Shard of the Naaru
Rustrot Viper
Thrive in the Shadows
Chaos Strike
Shadow Word: Devour
Irondeep Trogg
Renew
In 2 Decks
Hand of A'dal
Gift of Luminance
Intrepid Initiate
Wolpertinger
Raise Dead
Trueaim Crescent
Demon Companion
Adorable Infestation
Immolation Aura
Cutting Class
Cult Neophyte
Trampling Rhino
Rinling's Rifle
Illidari Studies
Blademaster Samuro
Piercing Shot
Desperate Prayer
Knight of Anointment
Cariel Roame
Warsong Wrangler
Barak Kodobane
Fury (Rank 1)
Alliance Bannerman
Fel Barrage
Noble Mount
Aimed Shot
Battleground Battlemaster
Ramming Mount
Mr. Smite
Doggie Biscuit
Need for Greed
Amulet of Undying
Lightforged Cariel
Aldrachi Warblades
Spectral Sight
Quick Shot
Gift of the Naaru
Stonehearth Vindicator
Murgur Murgurgle
In 1 Decks
Aldor Attendant
Corsair Cache
Libram of Hope
Libram of Wisdom
Aldor Truthseeker
Psyche Split
Soul Mirror
Lady Liadrin
Pit Commander
Magtheridon
Secret Passage
Draconic Studies
Athletic Studies
Animated Broomstick
Wave of Apathy
Coerce
Lord Barov
Blessing of Authority
Devout Pupil
Fel Summoner
Glide
Felscream Blast
Cloak of Shadows
Swindle
Sword Eater
Feat of Strength
C'Thun, the Shattered
Nazmani Bloodweaver
Hysteria
Talented Arcanist
Power Word: Fortitude
Lightshower Elemental
Silverleaf Poison
Wicked Stab (Rank 1)
Paralytic Poison
Swinetusk Shank
Outrider's Axe
Mor'shan Elite
Conditioning (Rank 1)
Bulk Up
Taintheart Tormenter
Cleric of An'she
Mankrik
Garrote
SI:7 Extortion
Harbor Scamp
Final Showdown
Sigil of Alacrity
Jace Darkweaver
Elekk Mount
Maestra of the Masquerade