Dwarfs, mostly. Some particular examples:
* Gungnir: created by the Sons of Ivaldi (Prose Edda, p 145)
> Loki went to those dwarves who are called Ívaldi's Sons; and they made the hair, and Skídbladnir also, and the spear which became Odin's possession [Gungnir]
* Mjölnir: created by Eitri and Brokkr (Prose Edda, p 146)
> Then he [Eitri] took from the forge a hammer [Mjölnir], put all the precious works into the hands of Brokkr his brother...
* Dainsleif (Prose Edda, p. 189)
> Thou hast made this offer over-late, if thou wouldst make peace: for now I have drawn Dáinsleif, which the dwarves made
* Tyrfing: created by Dvalinn and Durin (Hervarar Saga (1. KAPÍTULI))
And just maybe Völundr (Wayland the Smith) (who forged Gram), who _might_ also have forged:
* Lævateinn (Viktor Rydberg’s Investigations into Germanic Mythology Vol. II)