I do think Rowan is unisex because I know boys and girls with the name. But people will no doubt start saying that Rowan is "too feminine" or "wet" for a boy. (I've seen comments like that about Robin, probably because Robyn has become popular for girls.)
Alex is a good unisex name because it could be short for Alexander or Alexandra. There must be other names like that... Chris for Christopher or Christina/Christine...