Hello! There are many great math websites you can use.

First lets start with http://www.quia.com/web
In the bottom right is the option for shared activities: http://www.quia.com/shared/
If you have a Quia account you can create your own activities, but even if you do not, you can use ones that others have made.
Search for links and email them to yourself of activities you think you would use next year.
Do a search for ALICE KEELER
I have contributed well over 300 activities to the site, plus I have at least another 200 I've made and not shared yet.

Another website that is great is to consider creating a moodle.  It is not specific to math, but it does let you use latex code if you want. The district has a district moodle.  Contact Chris Edmondson if you are interested.  
(Moodle will be demonstrated)
Moodle is a great (free) way to organize all your math activities and to track student progress.

Check out ALEKS.com.  While a little pricey, the schools get a pretty good group discount. 
 

www.funbrain.com has lots of great activities that are great for the math classroom.

www.math.com is a good overall resource.  This can be used while you lecture.  Have this up and work through the math.com site with students.

www.hippocampus.org was created by University of California to teach a variety of subjects, including math.  Interactive tutorials and lesson plans make this an excellent resource!

Check out this math toolbox, which tools can you use? http://www.themathlab.com/toolbox/toolbox.htm

Try www.sketchfu.com.  I have students draw their linear equations, one dimensional x  5 type graphs, etc... in a sketchfu and then copy and paste the url or embed code into my website to turn it in.  
When students turn in their drawings, I then am able to correct their drawing and they get notification of the correction.
Make sure you slow down the speed
http://sketchfu.com/drawing/1113199-correction-dotted-and-neg-slope
http://sketchfu.com/drawing/1105444-correction-negative-slope
http://sketchfu.com/drawing/1100164-y-less-than-or-equal-to-2
 

And for videos try www.teachertube.com or www.schooltube.com
http://www.teachertube.com/viewVideo.php?video_id=92704title=Proof_of_the_Quadratic_Formula_by_Completing_the_Square_SONGref=alicegop

http://www.teachertube.com/viewVideo.php?video_id=120454title=Like_Termsref=alicegop

http://www.teachertube.com/viewVideo.php?video_id=78998title=More_Multiplying_Rational_Expressions_Examplesref=alicegop

Schooltube video: http://got.im/C9Q

Search for videos you can put on your website!

http://www.clovisusd.k12.ca.us/chs/

Welcome to Math! This is my 11th school year teaching at Clovis High School.  I'm also a Clovis High Graduate, where I benefited from the amazing instruction of all the teachers here (many of whom are still teaching here).  I graduated from Fresno State with honors with a degree in mathematics.