ther Resources

Dan Isdell has created a Truetype font for designing Celtic knots. This allows you to quickly create knotwork in any Windows application that allows font selection.
(as a side bonus, you can draw a knot, convert it back into a standard font, and email the results as if it were plain text!)
Aidan Meehan presents his Celtic Design series online (also mentioned in the bibliography).
Steven Abbott has a small Visual Basic program which draws certain subclasses of knots (using the folded-strip method, but without the lines).
Drew Ivan has written up his instructions on how to draw Celtic knots. His method is adapted from Iain Bain's. He also has some other celtic resources.
Peter Gruhn wrote up a method he learned from some mysterious stranger named Sarah. It's a very freeform method, but it bears a strong similarity to mine...
Yoshiaki Araki used to have a list of knot resources, including some mathematical knot links. (but I can't find them there anymore...)
thau! presents a Java applet for doodling with Celtic knots. It's limited to fat-width knots with only small curves, but is fun to play with anyhow.