The first answer (by kenteroo) is excellent. I'd like to elaborate a little, though:

1. The first method described (using a neutral density filter) is applicable only if there is a clear straight line dividing the upper and lower parts of the scene. If the crag, for example, extends into the sky, then the filter would make the crag even darker than it already is.
    
2. HDR is a great technique (see example here). It requires that you take several consecutive shots (e.g. 3), each with a different exposure level (i.e. one normally exposed, one underexposed and one overexposed). You then use a special software such as Photomatix to combine the three shots. The best way to do this is by putting the camera on a tripod and setting the camera to "autobracketing mode", in which it takes three consecutive shots automatically with varying exposure levels. The problem is that very simple cameras may not have this autobracketing feature or even the option of manually adjusting the exposure.
    
3. HDR from a single shot (instead of from several combined shots) - this can be done if your camera can shoot in RAW mode. Again, this is something that many simple cameras cannot do.
    
4. Fill flash - adjust the exposure to the brightest part of the image, and use flash to illuminate the darker part. For example, suppose you want to shoot a person who is standing in front of a setting sun. Aim the camera to the bright horizon and lock the exposure (usually by half-pressing the shutter release button), then shoot with flash on. This will make sure the setting sun will come out nicely exposed (and not overexposed), while the flash lights up the person in the foreground. Of course, for this to work your subject has to be within the range of your flash (usually a few feet away).

I hope this helps. If you need any clarifications just let me know.