two variables correlation can be presented as smoothed color density plot

1. Here is an example:
(http://sas-and-r.blogspot.com/2011/07/example-92-transparency-and-bivariate.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+SASandR+%28SAS+and+R%29)
(please go to scatterSmooth function)

 

2. another example

http://princeofslides.blogspot.com/2011/02/fixing-up-smoothscatter-heat-maps.html