As a born and bred Norseman with a long interest in the vikings' culture and mythology, I feel I have to contribute some facts to all these guesses...
The Vanir and Aesir had a long history of minor squirmishes and quarrels, before Loke (the Jotnir who was allowed to be one of the aesir, because he was Odins friend and bloodbrother from before the creation of Aasgard) negotiated a pease treaty. The treaty included a trading of diplomats/hostages. The richest and the wisest from each side was to go and live with the enemy. The Aesir sent Mimir as their wisest and Honir as their richest. The Vanir sent Frigg (wise) and Njord (rich).
The trick was that the richest among the Aesir was really Odin and he absolutely wouldn't go. In fact, he was angry with Loke for negotiating such a ridiculous deal, and ordered Loke to think up a plan to get him out of it. Loke then enchanted a rooster to make it look and act like a man (Honir is ancient Norse for chicken-man!). The Vanir soon realized they'd been had, however, and killed both Honir and Mimir, sending their heads back to the Aesir. Mimr was then animated by Odin, and stayed in Odins hall Valhalla as a living head working as Odins advisor.
Njord (God of the Sea, sailors and fishermen) brought his two children Frey (God of Farming and animal husbandry) and Freya (Goddess of love and fertility) to Aasgard ('Aasgard' means 'stronghold of the Aesir', by the way).
Frigg married Odin and became Godess of wisdom, nature and animals. Together they had the children Thor (God of thunder), Brage (God of music, poetry and literature), Balder (god of art and all things beautiful) and Vidar (God of Justice and Revenge, and as strong as Thor himself! Proficies say he will be only Aesir to survive Ragnarok <the end of the world/judgement day> and will slay the giant wolf Fenris, after it has eaten the sun, the moon, Odin and a bunch of other Gods. He will then build/create a new, better world. Also, I'm named after him!

). Frigg and Odin also had several other children, but these are the most important ones.
I noticed there was mention of elves somewhere on this thread. Yes, according to myth, elves lived in the forests south os Aasgard. Even further south lived trolls and Jotnir, and really far south lived the horrible fire giants.
In the mountains to the north of Aasgard lived the dwarfes, the worlds greatest blacksmiths and creators of magic items. Mjoelnir (Hammer of Thor), Gugnir (Spear of Odin) and many other of the Aesirs most prized magic items were made by these dwarfes. Underneath these mountains, in vast dungeons and underground cities, lived the terrible, evil black elves...
Even further to the north was the arctic, mountainous land of the frostgiants.
Yes, it's a fact! The elves, the dwarves, trolls, giants and even drow of modern fantasy are all actually based on seventh century Norse mythology! (Hmm... Maybe Drizzt is really a fellow Norwegian?
