A really good vanilla, made with real vanlla beans and chocolate shavings woud top my list. It's a hard-to-come-by combination, and I find myself settling for something close most times.
Cat Cora, when she worked at Bistro Don Giovani in Napa, made a vanilla ice cream with fresh ground black pepper that blew us away. While unavailable commercially (AFAIK), it remains today my most memorable ice cream eating experience.
Another remarkable ice cream was Giuliano Bugialli's Sorbetto di Parmigiano. When I had it the first time, made by Judy Gruhen back in NYC some 30+ years ago, I was amazed by how "innovative" it was. I've long since come to learn that the idea, if not the precise recipe, goes back at least to the late 1700's, and since my first taste of Judy's creation, I've had several versions over the years.
