Gaussian

• Using Gaussian 94/98 at NIST. by Robert Bohn. A somewhat dated tutorial, but has good examples of exercises to do.
• Molecular Modeling CHEM 4560, by Kubelka. A pretty decent set of notes of molecular modelling.
• Quantum Theory Group, by Mark Gordon. Not really on Gaussian, but has a decent amount of quantum chemistry stuff.
• Basis Sets in Quantum Chemistry. by David Sherrill. A set of slides on basis sets

Frank Jensen. Introduction to Computational Chemistry.

Christopher Cramer. Essentials of Computational Chemistry.

James B. Foresman, AEleen Frisch. Exploring Chemistry with Electronic Structure Methods: A Guide to Using Gaussian.