Calculus textbook recommendation?

Spivak is good and well-loved and even has a sense of humor.

Note that there are two ways to learn calculus: the high-school way, without proofs (Stewart is a good example) and the college-level way, with epsilon-delta proofs (Spivak is this kind.) You should decide what fits your needs best. You don't necessarily need to learn high-school-style calculus first -- my first intro to calculus was Serge Lang's book, which is similar to Spivak but more compressed -- but if you're just getting started computing derivatives it may help to do some physics problems to build intuition.

Yes, Khan Academy got everything you need. Also see Just Math Tutotrials and A Gentle Introduction To Learning Calculus. And here are lots of free Calculus books.

Ugh. I remember Stewart. It was all formalism and high-handed discussion of concept, and little in the way of concrete examples. A lot of the learning came from working through the exercises, which is frustrating for obvious reasons. It is thorough, however, and will teach the foundations.

For someone who isn't as interested in formalism, I would recommend Larson, Hostetler, and Edwards (just find an old edition at a used book store). It's geared toward advanced high-school math and had (in my edition at least) a review of pre-calculus/trigonometry, so it might work better for your purposes. Best of luck!