Bah! How's about all the spline types, broken down into immediate-to-use code, with easy to understand explainers showing how they are all related?

http://www.cubic.org/docs/hermite.htm

Wow, this is amazing! Much more detailed than my own interactive Bézier curves demo:

http://www.jasondavies.com/animated-bezier/

A lot of material about Bézier curves here: http://www.tinaja.com/cubic01.asp

All well and nice, but it doesn't explain how to actually DRAW something! I used to write a lot of text in Latex, and used metapost/tikz/pgf to draw box and arrows diagrams. Drawing straight lines was OK, but trying to make nice curved arrows going around nodes was a PITA and based mostly on experimenting. I knew where to find the math behind Bezier curves, but it was (and still is!) mostly useless from the perspective of a "end-user" not using a GUI.

wow, more than i was expecting.

Some of the figures take longer to load than desired, but the presentation is really nice.

I'm currently in a curves & splines course, this will make excellent review material right before the final in a couple weeks. Thanks! (As well as to all the other commenters here sharing other resources.)

And here I thought the site was only about the Japanese language. That's a nice tutorial.

The main site has a lot of information on studying Japanese for those who are into that sort of thing, BTW.

I use bezier curves to animate these tentacles: http://www.youtube.com/watch?v=RMwJXP8EOU4