Splus

Chambers and Hastie T., Statistical Models with S, Wadsworth and Brooks.
Ripley B. and Venables W., Modern Applied Statistics with Splus, Springer and Verlag. http://www.stats.ox.ac.uk/~ripley/MASS/
Spector Ph.,An Introduction to S and Splus, Duxbury Press, California.

Here is some online documentation sites:
http://www.cs.dal.ca/splus/contents.html http://yates.coph.usf.edu/~yiliang/sys/splus.html

http://www.maths.lancs.ac.uk:2080/~maa017/Splus/Intro/intro.html

The very long postscript files that were written before the Springer book of Venables and Ripleys are available at : http://www.math.montana.edu/stat/tutorials/Splus.html

A short handout that explains clearly how to start using Splus: http://www.ms.washington.edu/help/software/splus.html

The most colorful page on Splus I found: http://boserup.qal.berkeley.edu/~carlm/213/Week1/