Windside of Finland have been making their vertical wind turbines since 1982. The turbines have no sound emission they claim, 0dB due to their vertical arrangement rather than the traditional horizontal propeller arrangement.
They have eight models available, ranging from a small model to suit buoys through to larger commercial models.
Due to their configuration they will take up less space than a propeller type and certainly look better.
Their homepage has a cool little video of one of the turbines in action.
No prices seem to be on their website, so you will have to contact your nearest supplier.