UPDATED LIST:
Albania: Metalist
Argentina: Metaleros
Austria: Metler, Metal(l)er
Belgium: hard-rockeurs, Metal Heads, Hardrockers, Metallers
Brazil: Metaleiros
Bulgaria: Metali, Metalisti
Canada: Bangers, Metalleux / Metalleuse, (Dirties), (Pwel/Pouèle - only used in Quebec city)
Chile: Metaleros, Chascónes, Murciélagos
China: JinShuYueMi
Croatia: Metalci
Czech: Metalisti, Metly
Denmark: Rockers, Hammerheads, (direct translation: Metal-Hoved, but barely used)
England: Metalheads, Greebos, (Goffs - rather referring to Goths)
Estonia: Metallifännid
Finland: Metallisti, Hevari, Metallipää (?)
France: Métalleurs, Métalleux / Metalleuse, (Hardrockers)
Germany: Metal(l)er, Heavies
Greece: Metallades
Hungary: Metalosok, Rockerek
Iceland: Metalhaus, Rokkari
Israel: Metalistim
Italy: Metallari
India: Metalheads, Metchulhead
Klingon: baSnach
Lithuania: Metalistai
Luxembourg: Metal(l)er
Mexico: Metaleros
Netherlands: Hardrockers, Hardsnokkers, Metaal Hoofden
New Zealand: Metallers, Munters, Slammers, (Bogans)
Norway: Hardrocker, Metalhuer, (direct translation: Metalhode, but barely used)
Portugal: Metaleiros
Puerto Rico: Metallicos
Romania: Metalisti / Metalishti
Russia: Metalisti, Metalyuga
Slovenia: Metalci
Spain: Metaleros, Jevos, Heavies
Sweden: Hårdrockare, (direct translation: Metallare, but barely used)
Tunisia: Hredsa
Turkey: Metalci
Ukraine: Metalist
USA: Metalheads, Headbangers
Serbia & Montenegro: Metalci
some languages still missing...