i wish you allowed for more than one voting.
Star Wars isnt a trilogy anymore, its a 6-part saga. complain what you want with the prequels, but they are linked to the originals the way the originals are linked to the prequels. they cannot be separated. not anymore.
Spiderman will be taken off that list soon because of the 4th movie efforts (which they have to, since the 3rd didnt really feel like an ending).
the same goes with Jurassic Park.
Indiana Jones has technically stopped being a trilogy since they started shooting the 4th movie last month.
so for me that just leaves:
The Lord of the Rings trilogy
The Godfather trilogy
Back to the Future Trilogy