There are a number of free R tutorials available, and several (not free) books that have good information. For more recommendations look at the CRAN contributed area.

Online Tutorials

  1. This free R tutorial by DataCamp is a great way to get started.
  2. If you're already somewhat advanced in R and interested in machine learning, try this: Kaggle Tutorial on who survived the Titanic.

PDF Tutorials

Each of the following tutorials are in PDF format.

  1. P. Kuhnert & B. Venables, An Introduction to R: Software for Statistical Modeling & Computing [zipped]
  2. J.H. Maindonald, Using R for Data Analysis and Graphics
  3. B. Muenchen, R for SAS and SPSS Users **
  4. W.J. Owen, The R Guide
  5. D. Rossiter, Introduction to the R Project for Statistical Computing for Use at the ITC
  6. W.N. Venebles & D. M. Smith, An Introduction to R **

Books

The following books are available for purchase online. Amazon provides a preview of each book's contents.

  1. M. Crawley, Basic Statistics: An Introduction using R
  2. P. Dalgaard, Introductory Statistics with R
  3. B.S. Everitt & T. Hothorn, A Handbook of Statistical Analyses Using R (2nd ed.) **
  4. J.J. Faraway, Linear Models with R
  5. J.J. Faraway, Extending the Linear Model with R: Generalized Linear, Mixed Effects and Nonparametric Regression Models
  6. J. Maindonald & J. Braun, Data Analysis and Graphics Using R: An Example-based Approach
  7. P. Murrell, R Graphics (2nd ed.)

** Much of the inspiration for this site came from these texts.
I highly recommend them!!