arrangement of crowded labels

...
Thanks for your answers. This was almost what I was looking for, except that I 
would need something for a 2-dimensional context (my question was not specific 
enough).
  

Hi Thomas,
The thigmophobe.labels function just works out how to place each label 
away from the nearest point to the point that is being labeled. The 
pointLabel function in the maptools package and the spread.labs function 
in Teaching Demos use more sophisticated algorithms to do this, and may 
work in situations where thigmophobe.labels wouldn't separate all the 
labels.

Jim