Sebastian is an ancient martyr's name turned literary, and Little Mermaid hero—think Sebastian the Crab—that's more popular than ever, as a classic-yet-unconventional compatriot for fellow British favorites T Theodore and Oliver.

Crosby is an attractively laid-back Irish surname with retro musical associations to Bing and Crosby, Stills, and Nash, and with a jaunty air. Crosby Braverman was the name of a character on the TV show Parenthood, played by Dax Shepard.

According to Irish legend, Saint Brendan the Voyager was the first European to touch American soil, and his name has been established here for decades, peaking in the late 1990s.

Brennan is a winning Irish surname name, more modern than Brian or Brendan, more unusual than Conor and Aidan. The only possible problem with Brennan: people might think you're saying Brendan.