I personally love the Crystal Explosion flexible belly button rings. These are longer than your average belly button ring and many people can wear these as maternity belly button rings too. These have been very hot this summer. These crystals do not fall out!!
I got in a big shipment today, and a few favorites are back in stock. If you are not pregnant, don't worry about the length. Simply snip the end off of the flexible shaft and screw the ball back on for a perfect and custom fit belly button ring. This photo shows it next to a standard 7/16 inch belly button ring. These are great if you have a deep piercing too.
I forgot to mention, these are only $11.99 at BellyCharms.com.