For self-studying calculus, several recommended books cater to different needs. "How to Ace Calculus: A Streetwise Guide" is suggested for its informal approach to breaking down concepts. For a balance of theory and applications, "Calculus" by Courant and John is a classic choice. "Calculus Made Easy" by Silvanus P. Thompson is recommended for those seeking intuitive understanding without deep theory, particularly useful for engineers. For rigorous mathematical theory, texts by Apostol, Spivak, or Kitchen are ideal. The original "Calculus" by George B. Thomas, especially earlier editions from the 1960s or 1970s, is also noted for its effectiveness, along with the first edition of Edwards and Penney. Exploring library options or second-hand books can yield affordable finds.