Linear Technoloy's LTspice simulator is a free, very high performance Spice simulator that is very much appreciated by professional designers and serious hobbyists alike. Gilles Brocart has written an extensive book with reference material, applications information and simulation methods. The book has a preface by LTspice's development manager Mike Engelhardt.
Bob Cordell, an avid LTspice user himself, has reviewed this book for Linear Audio Volume 9.
The review is available for download free of charge. The book itself is published by Würth Electronic but they have agreed to make it available for Linear Audio readers in an English and a German version. You can get it in our store for slightly less than at the other places... ;-) .