I obtained five new books for the collection the other day. All are Ace paperback editions from the mid-1960s. They are: The Defiant Agents, Galactic Derelict, Plague Ship, Quest Crosstime, and Star Gate.
Quest Crosstime can also be seen in the Jack Gaughan section under Cover Artists; The Defiant Agents, Galactic Derelict and Star Gate can be seen in the Ed Emshwiller section.
New are Cover Artists Ed Emshwiller and Ed Valigursky, along with links that show Polish and German editions of Norton's books.