You can use your stunning attacks in rapid succession.
Prerequisites: Combat Reflexes, Stunning Fist, base attack bonus +6.Benefit: You may use one additional stunning attack (or other special attack that counts against your daily limit of stunning attacks) per round.
Normal: You may only attempt a stunning attack (or any other special attack that counts against your stunning attacks) once per round.
Special: a fighter may select Rapid Stunning as one of his fighter bonus feats.
A character can take this feat multiple times. Its effects stack.
Source: Complete Warrior, page 104.