Below is a shortlist just to make it easy to find all episodes.

Episode 21 : Enter! The World of the Shinigami
Episode 22 : The Man who Hates Shinigami
Episode 23 : The Sentence of Rukia, Before the 14th Day
Episode 24 : Assemble! The 13 Divisions
Episode 25 : Penetrate the Centre with an enormous bombshell?
Episode 26 : Formation! The Worst Tag
Episode 27 : Release the death blow!
Episode 28 : Orihime is Being Targeted
Episode 29 : Breakthrough! The Death God’s Encompassing Net
Episode 30 : Renji’s Confrontation
Episode 31 : The Resolution to Kill
Episode 32 : Stars and the Stray
Episode 33 : Miracle! The mysterious new hero
Episode 34 : Tragedy of Dawn
Episode 35 : Assassination of Aizen! The darkness which Approaches
Episode 36 : Kenpachi Zaraki Approaches!
Episode 37 : Reason of the Fist
Episode 38 : Desperation! The Broken Zangetsu
Episode 39 : The Man of Immortality
Episode 40 : The Shinigami whom Ganju Met
Episode 41 : Reunion, Ichigo and Rukia