TeachHub: Join the Teach Hub community for free and gain access to updated articles, blogs, lesson plans, and discussion forums. Sign up for weekly updates, start or participate in discussions, share what you are doing in your classroom, and connect with other teachers.
SimpleK12: Ok, this isn't actually a networking site, but it does have a blog and some free training via webinars for technology. There is plenty of free content and information, but also a paid version that gives you access to even more great training. Sign up for emails and be alerted when membership fees go on sale.
TeachAde: An online community for teachers to browse lesson plans, articles, and videos or connect with other teachers. Join groups and discussions and share your resources with others. TeachAde is free for K-12 educators with great resources.
Classroom 2.0: A social network for educators interested in technology to use in their classroom. Join in forums, view live training, and connect with other teachers to collaborate and share ideas. Really neat technology information at this site!
We The Teachers: Another social networking site to collaborate and share ideas with other educators. Free to join. Search for resources, tools, and groups to be a part of.
ISTE Connect: The International Society for Technology in Education has a place to connect with other educators using technology in their classrooms. Network with others via blogs, wikispaces, Twitter, and other social networks. ISTE does have a membership fee, but also has great information and resources for learning more about integrating technology.
Don't discount Facebook groups and Twitter as great ways to discussion education and share ideas as well. Check these out over the Summer as you prepare for next year. And really be sure to check out the webinars that some of these sites offer. I learn most of what I know about instructional technology through these trainings that I can view on my own time. You can view and learn from the comfort of your own couch!