MIT Open Course Ware has made the textbook Calculus by Professor Gilbert Strang available online. The book was published in 1991 and is still in print from Wellesley-Cambridge Press. It is a very useful resource for educators and self-learners alike. It is well organized, covers single variable and multivariable calculus in depth, and is rich with applications. There is also an online Instructor’s Manual and a student Study Guide.

Here you can find the book: Calculus