The Beretta M9 was a semi-automatic handgun manufactured by Beretta. It was the military specification version of the Beretta 92.
Mishko Suba lost a bet to Alexis Drazen and owed him three Beretta M9s, as mentioned in a file on Drazen's PDA. (Findings at CTU)
At Erno Tobias' apartment on Central Park West, Jack Bauer found a weapons cache including a Beretta M9 with a Knight's Armament silencer. He took the handgun and used it to kill one of Montel Tanner's thugs during a chase through Central Park. (Collateral Damage)