Source: Player's Handbook
You can cast a spell with a moment's thought.
Benefit: Casting a quickened spell is a free action. You can perform another action, even casting another spell, in the same round as you cast a quickened spell. You may only cast one quickened spell per round. A spell whose casting time is more than 1 full round cannot be quickened. A quickened spell uses up a spell slot four levels higher than the spell's actual level.
Special: This feat cannot be applied to any spell cast spontaneously (including sorcerer spells, bard spells, and cleric or druid spells cast spontaneously), since applying a metamagic feat to a spontaneously cast spell automatically increases the casting to a full-round action.