non aggressive

gobies ( citron, clown, watchman, sleeper etc)
cardinals (if kept singly unless mated)
some blennies
gramma
wrasses

then the less aggressive though have been know to be.....

ocellaris clowns (singly or mated pair)
percula clowns (singly or mated pair)
Chromis (personally had an agressive bunch best in odd numbered groups more than 3)
tangs (depends when added and tank size)