The only name that DH and I can agree on for soon-to-arrive DS is Karl. But we can't use Karl as it was the name of my paternal grandfather, whom my mother still hates hates hates despite the fact that he died over 25 years ago.
Charles is a great suggestion, but it was also the name of my cousin who died two weeks after birth and I'm not sure how I (or his mother would) feel about that.
Carlos would be awesome, but I don't think it would work the American side of the family. A white boy, speaking with a British accent called Carlos would raise a few eyebrows on the trips to visit Grandma!
Eli, Elliot, Henry, Owen are all on my short list.
Cal, or maybe Cal as a nn for Callum would be the closest I can think of
Names that sound a bit like Karl: Carter Carsten Clarke Clay Cyril Kael/Cael (pronounced Kale) Kyle Kalil/ Khalile (one of the sexiest men I have ever met was called this, but he was wearing a wedding ring <sobs>) Kier Kelly Kirk