These websites contain step by step instructions for familiarization with R. For the complete beginners, these websites will walk you through the basic operations and get you comfortable working with the command prompt.
The content is similar to that of the E-Books, but these aren't necessarily organized as books, and they aren't available as a PDF.
Intro to R by a team of Google Developers. This is a complete introduction containing 21 videos spread over 4 chapters. There's a lot of material here.
R Tutorial by Kelly Black - This tutorial is from the Clarkson University Department of Mathematics, and is a great initial introduction to R. Black includes sections on probability, linear least square regression & a couple of case studies. This is a very well written tutorial.
Kickstarting R by Jim Lemon - This is the tutorial available through CRAN. It's quite lengthy and covers a lot of material. Lemon includes sections on writing scripts, ANOVA, student's t-test and more. If you make it all the way through this document, you'll be quite familiar with R.
R Tutor by Chi Yau, Ph.D. - This website is a complement to Yau's Kindle E-Book, which is available for sale at Amazon. Don't be mislead though, this is not a fluffy marketing site. Yau offers sample code & background information on ANOVA, clusters & more. You definitely want to see this.
Quick R by Robert I. Kabacoff, Ph.D. - This site is also a complement to a book. Kabacoff includes a lot of information beyond the standard operations though. Included are sections on advanced statistics, advanced charting & more. This is definitely a quality resource.
R Twotorials by Anthony Damico - This site has a different approach than the others. Damico gives his tutorials in 2 minute segments. The site offers 90 videos on a wide variety of operations within R. If you watch more that a couple you'll likely grow weary of his peppy introduction, but don't let that get in the way, he has some good stuff here.