Casimir, a traditional name of Polish kings, could do quite well these days as we see the rise of Caspian, Cassius, Castiel, et. al. Like Leopold and Laszlo, Casimir is strong and worth considering if you've got an adventurous streak — and bet your son will too.

Ferelith is an unusual yet deeply-rooted Scottish girl's name, also found in ancient Ireland and drawn from the Gaelic Forbhlaith or Forbflaith. While it went through a period of dormancy after the Middle Ages, there are some modern women named Ferelith, including actress Ferelith Young and Princess of Denmark Anne Ferelith Fenella Bowes-Lyon.

Endellion is the name of an early saint who was a daughter of King Brychan and goddaughter of King Arthur whose life is commemorated by the Cornish village of St. Endellion. This intriguing ancient name was brought into modern usage by British Prime Minister David Cameron, who used it as one of the middle names for his fourth child, a baby girl.

Finlo is a name from the Isle of Man, deriving from that island's pagan sun god, Lugh. Given the popularity of all Finn names right now, Finlo could be a great alternative for people who love the "Fin" sound but want a more unusual name.