Long time back I created a few lists on facebook and over the time one of them became redundant. I was looking all over facebook about how to delete that list and ultimately stubled upon the right link.

1.click on Accounts
2.click edit friends

3. On the left, about half way down you will see the category "Lists"

4.click on the list you want to delete
5.click on "Delete List"

6.Confirm by clicking "Delete List"