Personally, I love album covers that have no reference to the artist or the album title - so for me the obvious choices would be the covers for Orchid, Morningrise and My Arms Your Hearse, all first press, sans logo and title. I'm not sure why, there's something about an album cover consisting purely of artwork and total anonymity. Now if only I could get my grubby mitts on first press copies of Morningrise and My Arms Your Hearse..
So I guess Ghost Reveries and the 2-disc edition of Blackwater Park also fall into this catagory, though Ghost Reveries does have a sticker with the name on the jewel-case, and if I'm not mistaken, Morningrise does too - I'm not sure about My Arms Your Hearse though.