To follow on from RexGig, whether a 50mm lens is worth it depends on what you wish to achieve.
You don't get better quality photos per se from having a lower f/stop (the quality of the glass and optics do that) but the benefit of a lower f/stop is that you can achieve a lower depth of field i.e. it is much easier to blur the background whilst keeping the subject in focus, both literally in terms of optics and in terms of your attention when you look at the photo.
If that is the effect you desire, it's very much worth considering getting a 50mm lens. The f/1.8 model is fantastic value for money but you should bear in mind that while it is pretty competent at f/1.8, its best sharpness is achieved at f/2.8 or more though even at f/2.8 you've got a much shallower depth of field than you can possibly achieve with the 18-55mm kit lens in the same surroundings. However, as he said, you'd need to determine if 50mm would be too tight, in which case the 35mm f/2 or 28mm f/1.8 may be better options though both cost considerably more money.
Adding to RexGig's comments about the crop factor, a "cropped-frame model" refers to the size of the sensor. It basically means that, in terms of coverage, the sensor's surface area is "cropped" from the surface area of a 35mm "full-frame" DSLR sensor, which in turn is based on the 35mm film format. If you check the link below, you'll see how it works in practice when you compare an image taken from a full-frame body to an image taken from a 1.6x crop factor body where both are taken at the same position and distance from the subject and at the same focal length.viewtopic.php?p=229883#p229883