Pyroblast or Fireball

This macro will cast Fireball when clicked or Pyroblast when used in conjunction with the shift key.

/cast [mod:shift] Pyroblast; Fireball

Spammable Arcane Missiles

This macro will prevent you from interrupting Arcane Missile when it's still casting.

/cast [nochanneling:Arcane Missiles] Arcane Missiles

Multi-Rank Frostbolt

This macro will cast Frostbolt when clicked or Frostbolt Rank 1 for kiting when used in conjunction with the shift key.

/cast [mod:shift] Frostbolt(Rank 1); Frostbolt

Ice Barrier and Mana Shield

This macro will cast Ice Barrier followed by Mana Shield.

/castsequence reset=30 Ice Barrier, Mana Shield

Flamestrike or Blizzard

This macro will cast Flamestrike when clicked or Blizzard when used in conjunction with the shift key.

/cast [mod:shift] Blizzard; Flamestrike

Multi-Rank Arcane Explosion

This macro will cast Arcane Explosion when clicked or Arcane Explosion Rank 1 when you are out of combat (useful for detecting stealth classes).

/cast [nocombat] Arcane Explosion(Rank 1); Arcane Explosion

Spammable Summon Pet and Attack

This macro will summon your pet and attack your current target, if pet is not already summoned.

/cast [nopet] Summon Water Elemental 
/stopmacro [target=pettarget, exists] 
/petattack

Summon Pet and Freeze

This macro will summon your pet and cast Freeze on your current target, if pet is not already summoned.

/cast [nopet] Summon Water Elemental; Freeze

Frost Nova and Freeze

This macro will cast Freeze when your pet is summoned and Frost Nova Rank 1 otherwise. To use Frost Nova Rank 1 while pet is summoned, click the macro with any modifier key. When pet expires, the cursor will automatically be reset. from any pet castable spells.

/cast [nopet] [pet, mod] Frost Nova(Rank 1); [pet, nomod] Freeze 
/run if not GetPetTimeRemaining() then ClearCursor() end

On-Demand Shatter

This macro will cast Freeze when pet is summoned followed by Frostbolt for a good Shatter combo.

/stopcasting 
/cast [pet] Freeze 
/cast Frostbolt