Classroom 2.0 www.classroom20.com 
Classroom 2.0 is a free, community-supported network for educators and social workers. It provides experience and good practice examples sorted by subject, tool, and area.

Khan Academy www.khanacademy.org
Khan Academy offers practice exercises and instructional videos.  It includes math, science, computer programming, history, art history, economics, and more. Lots of the contents are translated into many languages.

TeacherTube www.teachertube.com
An online community for sharing instructional videos 

OER Commons www.oercommons.org 
OER Commons is a freely accessible online library that allows teachers and others to search and discover open educational resources (OER) and other freely available instructional materials.