More applicable to secondary teachers, here is another site which is great for math exploration.
Looking for a fresh new lesson presentation platform? This may suit you. It looks neat to me, and the adding of Polls for feedback is a great idea.
High School Math, you say? How about this! Great for generating problems and helping students solve them sequentially.
What a great classroom idea!
An interesting new multidisciplinary school website concentrating on multimedia content.
Here is a collection of resources, both online and offline.
Did you pick up a math course this fall and need a few extra resources for your high flyers and lower learners? Give this one a try.