There are many different styles of bar grips. Grip variations can include ergonomic grips, these can give alternative places to relieve pressure and ideal for long rides. Lock-on type grips prevent the grips from rotating/moving when on the handlebars.
Handlebar grips are the point of contact for your hands and often over-looked, a good pair of grips will reduce your fatigue, increase your control and make your ride more enjoyable. There are a few types of grip fitment, Lock-on grips from Sunline or Lizard Skin are ideal for XC use as they won't slip and twist. Ergonomic handle bar grips from Ergon are immensely popular amongst leisure cyclists and tourers due to their increased contact area and shape.