Spell cards? Do you mean the Tarot Cards? 

The Binding of Isaac wiki's got a [pretty comprehensive (if slightly generalized, and minorly inaccurate) list][1].

    O The Fool	Teleports the player to the starting room for that floor.
	I The Magician	Gives you the use of Spoon Bender until you leave the current room.
	IV The Emperor	Teleports the player to the Boss Room.
	V The Hierophant	Spawns two soul hearts.
	VI The Lovers	Spawns two hearts.
	VII The Chariot	Gives you a single-shot use of My Little Unicorn.
	VIII Justice	Spawns bombs, hearts, coins, and keys around the player .
	IX The Hermit	Teleports the player to the Mini-boss Room, or the shop if a mini-boss room is not available.
	X Wheel of Fortune	Spawns a Slot Machine.
	XI Strength	Makes the player bigger, increasing maximum health and damage until the player leaves the room.
	XII The Hanged Man	Gives you the use of Transcendence until you leave the current room.
	XIII Death	Gives you the use of The Necronomicon.
	XIV Temperance	Spawns a Blood Donation Machine.
	XV The Devil	Gives you the use of Book of Belial until you leave the current room.
	XVI The Tower	Gives you the use of Anarchist's Cookbook.
	XVIII The Moon	Teleports the player to the Secret Room.
	XX Judgement	Spawns a beggar. If you have no money, spawns 1 heart, coin, bomb and key instead.
	XXI The World	Acts as a Treasure Map for the current level only.

Tarot Cards II, III, XVII, and XIX are not present in the game, for one reason or another.

Off the top of my head, I've had The Hermit transport me to a shop (instead of the mini-boss room), and The World actually has a greater effect than that of the treasure map (not only do you see the rooms, you also see what's in them).

  [1]: http://bindingofisaac.wikia.com/wiki/Tarot_Cards