For humor - how about meshing famous names... like if Holly married George W, she would become Holly Bush. Could be interesting with middle names or keeping last names in too. (I am sure you can make funnier ones, I had a niece named Holly so that one sticks in my head. I always teased her that she would marry a man named, Bush or Hobby or Day....)
For romance - a theme of successful historical marriages or cinematic love stories (with happy endings, of course). Ones that all the guests would know.
-Trix ( :