Thanks for the considered words from Tom, Jim and Trogdor The Burninator, the origins of the name lost in the mists of time?!
Tom mentioned several points that I'd like to comment on. The use of extra study books, written at a lower level, is a strategy that I see some local students use. Interstingly though its the more successful student who is using them. The student whom I encounter usually doesn't do this. They have the official text and maybe some printed lecture notes from the internet and thats it. I suspect in this case the problem isn't just the math but the concept of how to study math that is the problem.
I suppose I'll jump in to the world of the blog with a question: What do you consider to be a solid and accessible introductory textbook to calculus?
By Solid I mean: No gaps in coverage that leave the reader at a disadvantage because of unclear text and examples or outright missed topics.
By Accessible I mean: Written so the average student can expect to understand the concepts directly or with a small amount of help outside the classroom.