Minimum: allow period, apostrophe, and hyphen (.'-), which are often legitimate characters in names (eg. "Dr. Robert", "Mr. Jones", "Brigadier Lethbridge-Stewart", "OMG Bacon's favourite piggie").
Better: .'-#*,"()[]$@&^?/=_:;<>
Ideal: all alphanumeric and punctuation characters in the common+latin range, plus space.
Even better, but possibly risky: all alphanumeric and punctuation characters in unicode, plus space.