This comes from a Michigander with a son named Benjamin Louis. She wants something classic that flows well with Benjamin but nothing trendy. So any surnames (Tucker, Wilson) are out as well as anything that rhymes with maiden. ;)
Her girl name is already picked out but I offered to throw some suggestions out there for fun. The middle name for a girl would be Louisa (love it!) or Louise.
Desmond (I like the nickname Des)
Theodore (Theo or Teddy are cute nicknames)
And some bonus girl names are Jane (I think Louisa Jane is really quaint and cute), Violet, Madeline, Margaret (Maggie Lou!), Jillian, Vivian, Audrey, Claire and Hope.
I tend to like one syllable names as middle names with longer first names--like Louisa Jane. But if the middle name were Louise and only two syllables it's fair game--Jillian Louise has a nice flow.