Though not strictly speaking a jewel, I do like the tiara-like quality of this headpiece by milliner Gigi Burris.

It is made with hand twisted feathers on a velvet band and has a certain charming Cindy Lou Who look to it.  In fact, I could see the chic residents of Whoville happily wearing this… not to mention real-life chic types.

This sells for USD $250 on Burris’s site.