There's actually nine:

- Vanaheim, home of the Vanir, a group of gods associated with fertility.

- Asgård, home of the Aesir, the big-name gods (Thor, Odin, Freya, etc.).

- Jötunheim, home of the Giants.

- Alfheim, home of the elves.

- Helheim, the underworld ("Hell").

- Svartalfheim / Nidavellir, home of the dwarves.

- Midgård, home of the humans.

- Muspelheim, home of fire elementals.

- Niflheim, world of mists.

(This is the commonly accepted list, but it's always worth mentioning that surviving literary sources of Norse mythology are very scarce. Much of the lore was reconstructed in the 19th century.)