
Presents a guide to the R computer language, covering such topics as the user interface, packages, syntax, objects, functions, object-oriented programming, data sets, lattice graphics, regression models, and bioconductor.
As others have mentioned, getting into the useful data structures and libraries is the next step here, because those are what makes R great. The book "R in a Nutshell" is a nice desktop reference, and the CRAN Task Views for your domain are a pretty helpful jumping off point: http://cran.r-project.org/web/views/
The R mailing list and Stack Overflow communities are also a tremendous resources.
One invaluable resource I forgot to point out was: http://www.statmethods.net/ Very concise, directed pages that help you understand common/acceptable ways to do specific things.
For plotting, I usually skip the base R plots and go with ggplot2.