My favourites, some mentioned already:
Gareth, Gabriel, Gideon, Gavin
Alan, Alain, Alaric, Alastair/Alasdair, Antoine
Leon, Leandro, Leander, Lysander
My first thought was Marius. I'm super biased because I've loved it for like, 10 years but still, I think it works.
Tobias, Julius, Peregrine, Percival, Arthur, Gwaine, Lucas, Cyrus, Amadeus, Thor, Roman, Dane, Cato, Anthony, Silas, Elias, Caius, Perseus, Zachariah, Vincent, Nathaniel, Timothy, Edmund, Justus, Cyprian, Tiberius? Hope some of these have helped :)