These are some websites containing good expositions of
relatively simple Mathematics, demystifications of complicated
Mathematics and other things in similar spirit.
David Joyce's Homepage, with beautiful lessons to teach basic ideas in Mathematics that seem like the way these subject could've been studied when they were "real" Mathematical topics and not "just tools" for more advanced Mathematics, as we see them today.
TeX THE WORLD, a plug-in that allows you to use TeX
formulas in ANY website (like gmail, google chat, forums, chat rooms,
etc).
Twiddla. A whiteboard to talk
about Mathematics
with people in other place while on the phone at the same time. This can be used with TeX THE WORLD to type math formulas on the board.