by Leslie Lamport, the creator of LaTeX (not of TeX ). Available from several places including: Emerson.
A Gentle Introduction to TeX , by Michael Doob, (mdoob@ccu.umanitoba.ca) is an introduction to (plain) TeX for "rank beginners". This file is not difficult to find on the Web (search for "gentle.tex"); alternatively here is a copy: gentle.tex, gentle.dvi, gentle.ps.
Essential LaTeX , by Jon Warbrick, is an attempt to give you all the essential information that you will need in order to use LaTeX . Only very basic features are covered... Available from CTAN (under info/latex-essential/, and here: dvi, postscript.
An Introduction To TeX And Friends, by Gavin Maltby (gmaltby@unpcs1.cs.unp.ac.za, maltby@unpsun1.cc.unp.ac.za), is an introduction to the TeX world through LaTeX : covers text processing and mathematical typesetting. Around 80 pages. Intended for LaTeX beginners, especially those who want to typeset mathematics and proceed to AmSLaTeX .
The Not So Short Introduction to LaTeX 2e is available from CTAN (under info/lshort), and here: lshort.dvi, lshort.ps.