I've always had a soft spot for unisex names for girls - especially names predominantly used as a boy's name (ie. Elliot, Sawyer). Now, I'm sort of interested in the opposite - unisex names predominantly used for girls, only using them for a boy.
The biggest ones that come to mind to me are:
Loren/Lauren
Leslie
Ashley
Ariel
I'm curious to see how many more we can come up with