Subscribe (electronic or paper your choice) to at least one the following newsletters:
Eightysomething! http://www.ti.com/calc/docs/80xthing.htm
This is published by Texas Instruments 3 times per year and contains graphing calculator tips and lesson ideas. Check out the TI graphing calculators link as well.
The Caliber http://www.vernier.com/caliper/index.html
This is published twice a year and contains new product announcements for math and science probes and software. Check out their home page as well.
Math Solutions http://www.mathsolutions.com/mb/frames/n_newsletter_frame.html
This is published by Marilyn Burns twice a year with math ideas for K-8 grades. There are many books recommended in this newsletter, which happen to be written by Marilyn Burns.
Eisenhower National Clearinghouse (ENC) focus http://enc.org/register/1,1686,,00.shtm
Published four times per year by the Federal Government. The magazine covers themes such as Innovative Curriculum Materials, Inquiry and Problem Solving, Integrating Educational Technology in the Classroom, Teacher Change, and Assessment in Mathematics and Science Education.
Student Math Notes within the Dialogue Newsletter http://www.nctm.org/publications/smn
Published 9 times per year by the National Council of Teachers of Mathematics. Contains ready to use secondary math lesson plans.