[R] Managing size of plots with many points

[Spencer Graves]

What is available to limit obvious overplotting, e.g. with a million 
points?  My primary motivation is to produce plots from R and S-Plus 
that occupy minimal hard drive space without sacrificing visual clarity. 
  (I've crashed MicroSoft PowerPoint by including plots that are too big.)

Right now, I can think of three different scenarios:

	  1.  Monotonic applications such as a normal probability plot.

	  2.  Lines (or connected dots).

	  3.  General scatterplots.

Several approaches have been suggested, and I've implemented an ugly 
algorithm.  However, I believe something better should be available, but 
I don't even know what words to use in a search.

Ideas?
Thanks,
Spencer Graves