Computing Information

Unix cheat sheet

Java cheat sheet

Good reference books:

LINUX in A Nutshell: A Desktop Quick Reference (3rd Edition)

Covers just about everything you'll need to know about Unix/Linux for years to come, including shell scripts, emacs, awk (also called gawk), and grep - except for gnuplot.  This is not a tutorial, but rather a reference manual.

Unix C Shell Field Guide

A more readable tutorial introduction to Csh scripting.

Java in a Nutshell: A Desktop Quick Reference

A must have reference book.  Chapters 1, 2, and 3 provide a nice short introduction to Java.

Java Examples in a Nutshell: A Tutorial Companion to Java in a Nutshell (Nutshell Handbook)

Just what it says.  Lots of good examples and recipes.

Gnuplot

is the standard tool for generating graphs and plots under Linux, but has no graphical interface itself.  Online manuals and tutorials include