A collection of Korean superstitions:

The web archive of Rike’s superstition page (because the original page has disappeared) features a list of superstitions gathered by ESL teachers in Korea:

The Number 4
When you go to the store to buy your first set of dishes, you’ll only find sets of five or more. You pretty much cannot get anything in a set of four. This is because the Korean word for 4 is pronounced like the Chinese word for death.

This Kimchi Mamas page on superstitions, and especially the comments that follow, is full of them!

Don’t wear white ribbons in your hair because it is bad luck. White is the color associated with funerals and death.

And some more superstitions from Korea:

There is also a superstition about the Korean magpie (bird). People say: If you see a magpie in the morning, you’ll get good news. In Korean folk songs, there are some stories about this bird. There is a song about this.

(Thanks to Joeys ESL Room)