You can cast a spell with a moment’s thought.
Benefit: Casting a quickened spell is a swift action. You can perform another action, even casting another spell, in the same round as you cast a quickened spell. You may cast only one quickened spell per round. A spell whose casting time is more than 1 full round action cannot be quickened. A quickened spell uses up a spell slot four levels higher than the spell’s actual level. Casting a quickened spell doesn’t provoke an attack of opportunity.
Special: This feat can’t 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 time to a full-round action.
Note: Casting a quickened spell was changed from a free action to a swift action in Complete Arcane pg 86. The update is reflected in the SRD and the Rules Compendium, but the reprinted Premium Player’s Handbook was not corrected. This omission was corrected in the reprinted Premium Spell Compendium (pg 4) where the details on swift and immediate actions are discussed along with a specific statement that casting a quickened spell is a swift action and that replaces what is printed in the Player’s Handbook.
Source: Player’s Handbook (Page 98)