I am helping you - it's just not really possible for us to pick fish for you - what if you don't like our selection? You have to educate yourself as to your possabilities.
For instance I will never recommend anyone to get common or perc clowns as frankly I don't like them, and I'm not thrilled by gobies either. But any of the larger, more interesting clowns is a bit big for a 20. I do like dwarf angels, and I think you should get a bicolour blenny, give the tank another 3 or 4 months without any more fish, then get a centropyge argi or similar.