I think I was the one that mentioned the German Butterballs -- and they are definitely my new favorite! The plants were taller than the other varieties that I had (Red Gold and Russet Burbank) and I was afraid there wouldn't be anything under all that greenery, but they were VERY productive, had nice regular oval shapes, and I haven't found one yet, of any size, with a hollow middle. They have a beautiful golden-colored flesh and are great for mashing, frying, baking, and pretty much any other use. Still too early to tell right now, but the friends that recommended them to me said they kept very well over the winter for them.
I plant my potatoes about a foot apart, in trenches about 10-12" deep, and then cover them only partially and keep filling in the dirt as the plants grow. Dig some for new potatoes, then dig the rest once the plants start dying back.