Hi! I'm a math teacher too.
I don't use the internet much to get handouts and such. We've got a crapload of books and stuff here luckily. I'm sure somebody else will chip in with advice on those types of sites.
As far as teaching techniques go, I've found these math teaching videos very instructional for developing my own presentations:
YouTube - yourteachermathhelp's Channel
Lately, I've been using some of the calculation and graphing features in class from this new website: