Click here for a Youtube playlist of Google Classroom Tutorials by Google Education
Google is offering advanced access to Hangouts video-conferencing capabilities. This includes up to 250 participants and the ability to record.
There is a free version that you can sign up for using a Google account. The free version has a 40-minute limit on meetings with 3 or more participants
Skype allows you to start a conference call using an invitation code with no account creation required.