Charilaos Aneziris's web site speaks for itself. It is a must for those interested in Knot Theory.
Rob Scharein's KnotPlot Site delivers the epitome of knot graphics. Of course, we believe our knots would be beautiful too if we were using his KnotPlot software. Alas, we could not, so go on over and check his out.
Eric's Treasure Trove of Mathematics has an absolutely breathtaking amount of information in the field of mathematics.
The Geometry Center is a wonderful resource for the advanced studies of geometry.
The Exploratorium is a fun place for science education.
Peter Suber's Knots on the Web is an extensive list of resources on knots of all types. His is the best resource for finding knots on the web.
Although the texts are not available online, some of you may be interested in World Scientific's Series on Knots and Everything, a collection of twenty in-depth volumes, or their Journal of Knot Theory and its Ramification (JKTR), edited by Louis Kauffman.