Furnace

Ore is worthless until you can smelt it, so this goes up in your starter base almost immediately. It throws off light, but a room built around one still will not count as valid housing, so do not plan an NPC bedroom with a furnace as the only fixture.

Every later smelter does everything this one does and adds more on top. Once a Hellforge is in your crafting corner the plain furnace is only there for decoration, and the Hardmode forges continue the same pattern. If the Merchant has moved into a jungle house he will sell you one outright for pocket change, which beats mining a pile of stone when you are setting up a second base out there.