Here is a map I just finished up (3 hours of flying around the city later) of all the heli pads. Each are individually marked (even the 5 in Algonquin) and even though this may seem irrelevant to some the devoted GTA pilots may find this interesting.
The only helipad on the map that is not clearly visible (marked as helipad) is the one on top of the Casino in North Alderney (Westdyke).
Some helipads have helicopters on them. It depends on the time of day, if your in single or multiplayer, at what point in the story your at.
(the one on the FAR FAR FAR left of the map won't go away IT DOESN'T EXIST)
Edited by FiendJager666, 02 July 2008 - 10:14 PM.