I only know of one. Douglass was a girl's name in Renaissance England, but it apparently fell out of favor altogether and disappeared from the name pool. In the mid-19th C Douglas cropped up as a boy's name, from the custom of turning the mother's maiden name into a given name for her son. (Or, in case of US Civil War veterans, the name of one's commanding officer.)
Interesting. I did a quick search on this
For Boy -> Girl there's a whole lot - Alexis, Addison, Ashley, Allison, Aubrey, Avery, Bailey, Beverly, Blair, Cassidy, Evelyn, Hilary, Kelly, Kelsey, Kennedy, Kim, Lauren, Leigh, Lesley, Lindsay, Lynn, Madison, Meredith, Morgan, Robin, Shannon, Sandy, Shelly, Stacy, Sydney, Taylor, Vivian, Whitney, Tracy.
For Girl -> Boy, very few. Examples are Jean and Frankie - the first is a male name in France, while the second, as a short for Francesca or Frances, has fallen out of favour for girls more than it's risen in popularity for boys.
There are a fair number of unisex names, particularly when you include sound-alikes (Aaron/Erin, etc) and names which were originally nicknames that came from both male and female names (Bobby, Chris, Jo(e), Toni/Tony.
There are also cultural cross-confusions. In English, you get the female Danielle and Nicola and the male Daniel and Nicholas. In Spanish, the male is pronounced Danielle but spelled Daniel, and the female is Daniella, while in French, Nicholas is pronounced Nicola (both cases are friends of mine). I also know Chinese men with English names of Bambi and Hope, which is a somewhat different story.