The Swift is a helicopter returning from earlier GTA games. Rockstar first showed it in an official screenshot (Vice City 03).
Buzzard Attack Chopper
The Buzzard Attack Chopper is a Nagasaki helicopter returning from earlier GTA games.
Maverick
The Maverick is a helicopter returning from earlier GTA games.
Police Maverick
The Police Maverick is a helicopter returning from earlier GTA games.
Sea Sparrow
The Sea Sparrow is a helicopter returning from earlier GTA games.