Just saw a great little video on http://www.unclutter.com/.
using the removable adhesive hooks ffancy ones or non fancy and put them on the wall inside the closet, or door or even on the wall inside the room. I love this idea I just finished doing for me in my 2nd bedroom/dressing room.
The other idea is to use old ice cube trays to put paired earrings inside the cubes and then stack them for vertical storage.