The following books will provide additional information about TeX and LaTeX. They have been listed because they are books that are either owned by people in the department or are available at the Gothic Bookstore.
LaTeX
The true LaTeX bible is LaTeX: A Documentation Preparation System, written by Leslie Lamport, the author of LaTeX. There have also been three companion volumes written by members of the LaTeX Documentation Project.
LaTeX : A Documentation Preparation System
Leslie Lamport
The LaTeX Companion
Michel Goossens, Frank Mittelbach, Alexander
Samarin
The LaTeX Graphics Companion
Michel Goossens, Frank Mittelbach, Sebastian
Rahtz
The LaTeX Web Companion
Michel Goossens, Sebastian Rahtz

Donald Knuth is the original author of TeX and his book is a must read for those aspiring to be true TeX wizards. Included among the wealth of information is the correct pronunciation of "TeX", and the proper name for a TeX guru  it's "TeXnician"! Michael Spivak wrote a very helpful supplement for using AMSTeX, "The Joy of TeX".
The TeXbook
Donald E. Knuth
The Joy of TeX
Michael Spivak

Mathematical TeX by Example
Arvind Borde
LaTeX Line by Line: Tips and Techniques for
Document Processing
Antoni Diller
LaTeX Line by Line: Tips and Techniques for
Document Processing (2nd Edition)
Antoni Diller
Math into LaTeX: An Introduction to LaTeX and
AMSLaTeX
George Gratzer
A Guide to LaTeX2e: Document Preparation for
Beginners and Advanced Users
Helmut Kopka and Patrick W. Daly
TeX for the Impatient
Paul W. Abrahams, Karl Berry
TeX: Starting from 1
Michael Doob
LaTeX for Everyone: A Reference Guide and Tutorial
for Typesetting Documents Using a Computer
Jane Hahn
LaTeX Notes: Practical Tips for Preparing Technical
Documents
J. Kenneth Shultis
TeX for the Beginner
Wynter Snow