The goal is to be able to pull it off without looking young (in an immature way). So this is what I found when I looked
The Beauty Department, Lauren Conrad and her friends' site, has a really cute idea
Zappos sells a bejeweled headband
The Rodarte hair accessory is a bit intense but still pretty cool. I don't think you can buy them because they were created in-house but this blog has done a DIY on them.
Simple hair pins with peals attached