Cursed Hat

As the name implies, a cursed hat will curse the person who wears it.

Bill Weasley once had a penfriend from Brazil who was offended when Bill couldn't travel all the way to South America for a visit, so this person sent him a cursed hat that made his ears shrivel up (GF7).

This is only mention of a cursed hat in the Potter universe, but it seems likely that hats can carry a variety of curses besides causing one's ears to shrivel up.