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.
Source: Player’s Handbook (version 3.5), page 98.