I dont know of any way to set the font for the basic title but a possible work around would be to use the UIView alternative. The navbar allows you to subclass UIView and use this in place of the title. With the View you would be free in incorporate text of what ever font you like, you could even make it multiple lines of any color etc. The world is wide open as long as the view fits in bar frame.
Of course since UILabel extends UIView you could use that as well as any other component derived from UIView. my point was that he has the full pectrum of flexability afforded by using a view, not specifically UIView.