clipped from: www.nationmaster.com   
Argentina

Juan Pérez, Don Nadie, Fulano, Mengano, Zutano or Sultano.

Australia

Fred Nerk, Joe Blow, Joe Bloggs, John Citizen, Joe Farnarkle, John Barry, Simon McCool

Canada

G. Raymond (male/female, mostly on credit cards and ID, used as could be either an anglophone or Francophone name), John Jones, Jos Bleau (Quebec, French adaptation of Joe Blow)

Japan

Dozaemon, a drowned corpse

Poland

N.N. ("unknown"--used to refer to e.g. unknown soldiers at war); Jan Kowalski, Jan Nowak (used in the meaning of "everyman", an average citizen)

Sweden

(Herr/Fru) Svensson, Medelsvensson for the average Swede; Kalle, Olle, Pelle, Nisse and Lisa are pretty common when a name is needed as an example. "Name Name" ( or NN from Latin Nomen Nescio) is used as a placeholder.

Slovenia

Janez Novak

South Africa

Koos van der Merwe, Piet Pompies

Nigeria

Lagbaja

Malta

Joe Borg

Italy

Mario Rossi, Pinco Pallino, Tal dei Tali, Tizio, Caio, Sempronio.

Croatia

Ivan Horvat, Pero Perić, N.N. ("Nepoznati Netko", trns. "Unknown someone")