An Asgardian, and the wife of Thor, Sif is famous for her long, beautiful golden hair. After Loki, the master of mischief, cut off her hair, new and magical hair was forged by enchanted dwarfs, who made it from real gold.
Sif is the mother of the Ull, the archer-god Ull. She is also the mother of Thrud. Curiously, she is not mentioned in the lists of goddesses or Asynjur given by the 13th Century Icelander Snorri Sturluson.
In the Eddic poem Lokasenna, when Sif tries to placate Loki with "mead from a crystal cup," but Loki rebuffs her.
Based on the tale Lokasenna she is sometimes invoked as a goddess of peaceweaving. This ties in well with her name which means 'kin' or 'relative'.
A common modern association for Sif is with the wheat harvest based on the tale of her golden hair. There is no ancient record of her links with the harvest.
A painting of Sif by Thorskegga Thorn can be found here.