Yeah, and just because one website says 55g is okay, that is not always correct. I have found that quite a bit while researching fish. I have a 120g, and some fish say 90g minimum, and then some on here say no less than 150 or 180! So ask around and make a well informed decision before buying any fish.
Some of my smaller favorites:
Clowns
Coral Beauty (angel)
Flame Angel
Banggai Cardinal
Pajama Cardinal
Mandarin Goby
Some wrasses...
Also note that the sizes listed on here are the size of the fish you are buying, not their potential size, so research that as well.