Whatever you want it to be - Freezers typically run at -18º C (0º F) because the pioneer of frozen food, Clarence Birdseye, decided that he liked the round number of 0.
The fridge compartment should be above zero and below 10º C - If you set it too low there may be cold spots in the fridge compartment that cause the food to freeze.
+4 or 5 ºC is normal - mine is set to 7º C to stop icing on the back wall.
Wikipedia has an article about Fridges that discusses temperatures.
Stay cool...
Peccavi, October 2009
