This is a particularly painful subject right now (I started my diet again last week, and have to stay away from any food that actually tastes good), but I still can dream about it, so I'll go ahead and comment on it.
So, my favorite screams would be:
Friendly's Butter Crunch
Mayfield's Moose Tracks
and pretty much anybody's Mint Chocolate Chip
great, I think I gained 4 pounds just thinking about this.