The Aesir and Vanir are the two sects of gods in Norse Mythology. The Aesir are the gods and goddesses of war, and the Vanir are the fertility gods. Eventually these two groups of deities entered a war against the other, and after much strife, the Aesir won out.

The Major Aesir Gods:
Odin- the chief god in Norse Mythology...in fact, one of his alternative names literally means "Allfather." He is the god of war, death, poetry, and wisdom.
Thor- son of Odin. God of thunder.
Hel- goddess of the underworld, Helheim. Daughter of Odin...the legend of Annis is sometimes thought to be contrived out of this goddess.
Loki- the son of giants...connected with magic and fire.

Tha Major Vanir Gods:
Freyr and Freyja- twin brother and sisters. god/goddess of fertility. The most noble duet in the pantheon of Norse Gods.
Njord- god of the sea. Father to Freyr and Freyja.
Nanna- the moon goddess, and i believe she may have been a mistress to Njord.