Metallurgy is a comprehensive restructuring of Minecraft's tier system for ore and stone. Basically it implements a large array of new ores (Copper, Tin, Bronze, Manganese, Steel, Mithril, Orichalcum, and Adamantine) and tweaks the old gameplay to try to make the game less about "digging as deep as you can to the bottom of the world as soon as you get stone tools".
For Minecraft 1.1
Metallurgy 1.2.3b Client.zip
Metallurgy 1.2.3b Server.zip
Metallurgy 1.2.3 Macerator.zip
zMetallurgy 1.2.3 Macerator Server.zip