This depends on you, what 18-105 offer is the through out zoom from 18mm to 105mm, but the kit lens covers 18-55mm zoom right, after that the 55-200mm lens kicks in.
the problem with 18-105 is that it has they same picture quality as of 18-55mm, n 55-200 lens but is expensive and has less reach, it won't give you sharp pics like the 50mm f1.8,
so why buy a 18-105 when the picture quality is gona be same,
the advantage of 18-105 is that if you cant carry around two lenses and you a person who shoots between different focal lengths and don't have time to change lens coz you are always in a hurry and 18-105 reach is all you need then buy the 18-105 you will be free of the hassle of changing lenses.. that's all