Also not counting those that can show up in any shape they want (Q, Prophets...).
That should disqualify the Changelings (Odo excepted).
The only three Changelings we got to meet a little better (Odo, Female Changeling and Laas) all had the same appearance in their solid/humanoid form, except for the short time when FC took Kira's form. That's what we've seen them look like most of the time.
OTOH, Q pretty much always took a human appearance, and had no specific other look (and it required no makeup or mask), and the Prophets had no corporeal form of their own and only ever took the appearance of people from Sisko's (or whoever else they were appearing to) life.