Miami is becoming very restricted, Fisher Island (was in there last week in a twin) is difficult to get into unless you or your PAX are connected, there is a golf course on South Beach and the Watson Island Heliport is officially closed by the City of Miami but still on the sectionals as X44 (Miami Seaplane Base).
Yes the Helipads at the Key Largo Marriott are very cool (the hotel restaurant is quite good also), the one in Marathon at the restaurant is a great lunchtime stop on a Key West Trip.
DT1 Helipad in Fort Lauderdale is certainly a must see and if its just a private flight certain Mosquito Control Helipads on the West Coast are also sometimes accesable with prior permission and arrangement.
I have a list of all private and commercial heliports in florida, drop me a PM and I will email it to you.
Geoff