Below are a bunch of resources to help you get acquainted with R, in no particular order:
Intro to R – A .pdf booklet introducing the basic functionality of R
Quick-R – A searchable website geared toward folks transitioning from SPSS
Stuff I wish I’d known when I started learning R – A blog post with some great tips for how to use R effectively, including a brief overview of good code practices, version control, etc.
R for Psych Research (from the Personality Project) – A guide to using R for psychological research, with translations between R and SPSS
http://experimentalfieldlinguistics.wordpress.com/links/statistics-and-r-blogs/ – A great list of resources for stats and R, targeted at linguistics (but probably fun for everyone).
http://www.screenr.com/Pps8 – An introduction to the R help documentation (video)
UCLA Guide – A compendium of useful beginner (and not so beginner) guides
Impatient R – A guide to help get you over “Blank Screen Syndrome”
Twotorials – a series of two-minute tutorials on R stuff.
Rice University – The syllabus and course materials for a stats class conducted in R from Rice
An excellent compilation of resources and tutorials: data_R
R-Project – The official R website
Excellent R package for multiple imputation (for missing data): Amelia
And, of course, where to get R if you don’t have it (this links to the Oregon State University mirror): http://ftp.osuosl.org/pub/cran/
If you find the blank screen too overwhelming, R Studio offers a free GUI for R (I, personally, find that R Studio is kind of clunky makes things more difficult, but that’s me -nml).
An awesome blog, asdfree.com (“Analyze Survey Data for Free”), with complete R instructions for finding, downloading, importing, and analyzing each of several publicly-available US government survey datasets.