Sparrow

The Sparrow is a small helicopter.  It's small and manueverable but does not have a machine gun like the Sea Sparrow.

One spawns on Madd Dogg's Mansion.

More info:
gta.wikia.com/wiki/Sparrow
https://www.grandtheftwiki.com/Sparrow

Sea Sparrow

 

The Seasparrow is a small helicopter equipped with floats.  It's small, maneuverable,  has a machine gun, and it can land anywhere.

One spawns north of the Verdant Meadows airfield, and another is near the dam.

More info:
gta.wikia.com/wiki/Sea_Sparrow
https://www.grandtheftwiki.com/Sea_Sparrow

Raindance

 

The Raindance is an emergency helicopter, presumably used to drop water on wildfires.

More info:

gta.wikia.com/wiki/Raindance 

https://www.grandtheftwiki.com/Raindance 

Police Maverick

The Police Maverick is a Maverick used by the police.  It has a machine gun.

One spawns on the roof of the police station in Los Santos.

More info:
gta.wikia.com/wiki/Police_Maverick
https://www.grandtheftwiki.com/Police_Maverick

News Chopper

 

The News Chopper is a helicopter.  It is a shorter version of the Maverick.  

The easiest way to get one is to steal it from the "Whirly Bird Waypoint" 'race'.

More info:
gta.wikia.com/wiki/News_Chopper
https://www.grandtheftwiki.com/News_Chopper

Maverick

The Maverick is a helicopter.  It's related to the Police Maverick and the News Chopper.

One spawns on the helipad on the north side of the San Fierro police station.

More info:
gta.wikia.com/wiki/Maverick
https://www.grandtheftwiki.com/Maverick

Leviathan

 

The Leviathan is a large, slow helicopter.

One spawns at the Verdant Meadows Airfield, another at the San Fierro airport.

More info:
gta.wikia.com/wiki/Leviathan
https://www.grandtheftwiki.com/Leviathan