I put my 11 yr old on this task last night. Here are her suggestions:
Yellow Belly Regal Blue Tang
Freckled Hawkfish
Orchid Dottyback
Azure Damsel
Tobacco Basslet
Striped Blenny
And she really likes the Curious Wormfish. Everything I've read about them says they're good in a reef tank. I think they're related to the engineer gobies, but I haven't heard if they burrow the same way. Not much info about them otherwise. Very tempted to try him at $35.