This is the book that this website is all about (paid link).
Getting Started with Latin My original Latin book, designed for beginniers, homeschoolers, and self-taught students (paid link).
Keep Going with Latin The sequel to Getting Started with Latin This book teaches you more Latin grammar while encouraging you to begin speaking Latin with friends and family (paid link).
Getting Started with Spanish My beginning Spanish book. This book was selected by The Well-Trained Mind as a top recommendation (paid link).
Easy French Step-by-Step is based on the idea that the quickest route to learning French is through a solid grounding in grammar basics. This is the bestselling French book on Amazon.com (paid link).
French Grammar Keep the rules of French grammar handy with this bestselling laminated chart (paid link).
501 French Verbs As you get more advanced in your French studies, you'll want to have a copy of this book around. On each page is a chart that shows all the forms of one particular verb (paid link).
The Well-Trained Mind: A Guide to Classical Education at Home This is perhaps the most popular homeschool curriculum guide available (paid link).