Gamma World Player's Handbook: A Campaign Setting for d20 Roleplaying, by Skellams, Geoff, Rautalahti, Mikko, Eller, Ian, Baugh, Bruce
Gamma World Science Fantasy Role-Playing Game/Boxed (3rd edition), by Ward, James M.
Legion of Gold (Gamma World Module, No. GW1), by Luke Gygax, Paul Reiche III, Gary Gygax
Referee's Screen and Mini-Module (Gamma World RPG 1st edition), by Paul Reiche III