Serena, a name used since Roman times, was given fresh life by tennis star Williams, and then again with the leading character on Gossip Girl, Serena van der Woodsen. There have also been Serenas on soap operas and other shows from Bewitched to Law & Order.

Seren, meaning "star", is one of the top girls' names in Wales, but as a boys' name it has a different derivation. It's a rare Polish form of the Latin Serenus, mostly used to refer to the Saint and meaning "serene". It could make for a handsome and almost unknown alternative to rising star Soren.

Both rhythmic and serene, Serenella is one of the Italian names for girls virtually unknown in the US but definitely usable. An unusual route to Ella as a short form?

Yasen is a male given name in Bulgaria with two lovely meanings — ash tree, and serene.

A name that's more familiar in its male form, Placido, but this can be a similar-feeling alternative to Serena.

Placido was commonly used by early Christians to convey their serenity in the faith, and it was borne by several minor saints.