I am listing some useful R resources. I start with the following post on (free) R Books from R-bloggers.com.
An R "Meta" Book by Joseph Rickert
This page lists some e-books or e-materials for various topics in statistics ranging from basis concepts of statistics to advanced methods such as survival analysis and time series analysis.
On Experimental Design
An R companion to ‘Experimental Design
This companion is by Vikneswaran. Topics include one and two factor experiments, multiple comparison, orthogonality, nested and hierarchical designs, Latin square and related three factor designs.
Creating R Packages
Creating R Packages: A Tutorial by Friedrich Leisch
This is a very basic yet useful introduction on how to create an R package. I highly recommend it for those who is new to writing R package.