Archwired has an incredible amount of material, including a Metal Mouth Message Board. I should post about Retainer Girl (also available at Amazon etc), though since the site is more for adults with braces the next Dr.Wrighting novel, Love and Braces, will probably be more interesting to them since it is about an adult with braces. (Retainer Girl is more for teens and adults who have been through the experience already, I think.)
There are also links to a lot of braces blogs there, which I will have to check out. And one more really interesting link I found there was to Smile (A Dental Drama) by Raina Telgemeier - a braces comic!
I've linked to some videos at Intraoral Press. The Head Gear Girl movie is impressive, but there's also a lot at Youtube. Like Retainer fun.