You may want to look at these two entries from 'SAS and R':
http://sas-and-r.blogspot.com/2011/07/example-91-scatterplots-with-binning.html
http://sas-and-r.blogspot.com/2011/07/example-92-transparency-and-bivariate.html
They cover the use of binning, transparency and bivariate kernel density estimators for scatter plots of large amounts of data. They might serve as decent starting points.
I'm rather biased against ggplot2, so I won't comment on whether or not you need to use it for prettyness - I find the figures in these entries to be perfectly appealing.