I haven't any children yet, but I've always liked the name Simon (after Simon de Montfort (1208-1265) - yes, crazy medieval historian here!!!). I'd choose William as a middle name, as it's my father's middle name and was my grandfather's name.
For a girl, I think Elen, Isobel or Leah. The first because it's a derivative of my grandma's middle name, Helen and also my sister's middle name, Ellen. Isobel - hmm, not sure, just like the name. Leah is a name I came across during my family tree research and although not a direct ancestor, I thought it'd be a lovely name for a child.