First of all, edweb.net. Not sure if many are familiar with this site, but edweb was established through support from Follett for librarians. It has grown into a much more intense site. You can see live webinars and access the archives for free. The content isn't just for librarians either. I have seen everything from teaching with games to mobile devices and iPads. There is a slew of information and it's all free. I have seen some excellent webinars and I have learned a lot of valuable information.
Secondly, simplek12. Simplek12 can be joined for free, but to access archives, you often have to have a membership. I spent about five days last summer watching some of their live webinars. The organization offers special programs, for example: there was a google day where the entire day focused on webinars about google, google docs, google chrome, google apps, etc. I have seen days about web 2.0 tools and days about iPads for the classroom. There are so many wonderful things on their site. It's loaded with ideas and content. The annual subscription payment allows you to access webinars in the archives. Some of them even have eBooks that relate. It's worth looking into the site, do some of the webinars, browse what is available and you will probably find justification for the site's fee.
These two sites are my go to places for webinars, but I have come across some other freebies as well: School Library Journal and Library Journal do free ones from time to time. Demco, the library supplier has a webinar series now. Even many DOE websites offer beneficial webinars that focus on our common core standards.