This problem can be solved with the Automatic Smooth Angle in the EditButtons, F9 menu. To render 'smooth' you have to do a 'Set Smooth' for the object, then turn on the 'Auto Smooth' option in the EditButtons. The effect of Automatic smoothing is only visible in rendering.
The number-button "Degr:" defines the maximum angle faces can make to be smoothed. This should be adjusted carefully so that no unwanted smoothing occours. For imported geometries it may also be necissairy to remove double vertices to achieve a propper effect.
The next image shows the effect on a cylinder, from left to right, not smoothed ('Set Solid'), just 'Set Smooth' and with 'Auto Smooth' (default Angle of 30°).