Tips for Success in Undergraduate Math Courses by Jessica Purcell. Some very good advice for college calculus students. Read this carefully and do as it suggests.
Common Errors in Undergraduate Mathematics by Eric Schechter
The calculus page problems list problems by D. A. Kouba at UC Davis
The Web page contains a plethora of interesting resources to help you visualize important mathematical concepts. Most of these are Java applets, which run interactively as plug-ins in your web browser. To use them you must have Java enabled in your browser preferences - by default, it probably is already.
And just for the fun of it, there's the Quadratic Formula Song (WMA - 1.1 MB).