18. M57, the Ring Nebula.  Formerly a red giant star, it's expelling its outer layers as it dies.

If you look closely to the lower right of the nebula, you can just barely see a faint galaxy (IC1296).  It looks like a star that is a little fuzzier than the others in this picture.  M57 is about 4 thousand light years away and the galaxy is about 200 million light years away.