tailspot blenny ftw!
not my image obviously
what are the dimensions of the tank? is it a 30g long or 30g high? if it is long there are wrasses you could be thinking about. i had a twinspot hog in my 30g and it did fine. firefish would also work and they are way cooler than cardinals or chromis. there are gobies like the yellow watchman that are quite neat.
id recommend going to the websites of the big online stores like liveaquaria, saltwaterfish, the marine center, ocean aquatics, etc and looking through the fish and checking their min tank requirements. youll want to take an avg of what the diff sites say, some will say angels can go in a 20g, others will say 50g. unforunately you will need to balance the conservative estimates to the liberal.