Re:Bassett's Ice Cream, Philadelphia
I love the butterscotch vanilla. I am also partial to their strawberry and their peanut butter vanilla.
Their website (bassettsicecream.com) has a section called Where to Find Bassett's Ice Cream with a list of all the store and "dipping parlors" which sell Bassett's (although some of the grocery stores have a very limited selection of flavors). If you want to bring some home from the Reading Terminal Market store, bring along a picnic cooler; they have dry ice available.
If you are planning on being out in the 'burbs when you visit, it's worth going out of your way to check out Longacre's Modern Daily Bar in Barto (reviewed on this site), as well. Or, if you're in the neighborhood, Handel's in Berwyn.