University of St. Andrews Math-History Site
Cornell University website for Math TAs
Tom Rishel's TA handbook at MAA (preliminary version, latest is a book for sale)
Inclusive teaching in math and science at UW
The Mathematics Genealogy Project
The Journal for Research in Mathematics Education list of web sites
Non-Euclid software for non-Euclidean geometry
Proof of the Four-Color Theorem
David Wilkins Math-History site
Journal of Online Mathematics and its Applications
UW-Madison site on Peer Review of Teaching
National Institute for Science Education, at UW-Madison
An interesting paper on inflation in grades and/or recommendations
NSF's Foundation Coalition is a national program integrating the educational experiences of beginning engineers and others: (UW-Madison and in particular the UW-Madison math department are participating in this)
MAA (Mathematical Association of America) (lots of other things too, but many education-related items)
AMS (American Mathematical Society) (lots of other things too, but many education-related items)
The Mathematics Archives (teaching materials section)
Mathematics and Education Reform forum
MAA committee on Calculus Reform and the First Two Years (Sometimes called CRAFTY)
The Connected Curriculum Project:
The Middle Atlantic Consortium for Mathematics and its Applications Throughout the Curriculum