Google Certified Educator Level 1 and Level 2 - You can use the training center to build your skills in using Google for Education tools in the classroom, even if you don't want to take the tests ($10-$25) for the official certifications.
EdCamps are free, participant-driven conferences. There are no presentations. Sessions are determined by participants on the day of the Edcamp and are based on discussion and collaboration.
Capella University - Free professional development courses for teachers. You can also earn graduate credit for an additional fee.
Class Central - Extensive listing of free Education & Teaching courses & MOOCs from universities and colleges.
Education Closet flipped workshops - Workshops for teachers are available to watch anytime on-demand.
EdWeb - Free webinars most days of the week on a variety of topics. Miss one? You can access webinars on-demand. They also have podcasts.
EdX - online courses on a broad range of topics. There are many you can access for free and optionally pay for a certification of completion.
Using social media to connect with other educators can be a great way to expand/share your ideas and learn from others who may have other perspectives or experiences.
Twitter chats are scheduled conversations (30-60 min on a specific days) on Twitter. They include the specific hashtag (e.g. #CAedchat) for that chat to help you follow the conversation during the chat. You can also search for that hashtag between chats to catch up on a conversation you may have missed.
Facebook groups are becoming popular now, also. Some are topic-based (e.g. equity in education, and STEM teaching ideas) while others are related to a specific tool (e.g. Google Classroom, See Saw, and Canva).
An Introduction to Twitter Education Chats - Edutopia
Extensive Twitter Chat Calendar
Just a few specific chats
Some Facebook chats are open to anyone. Others require approval from the moderator. This can be a good thing to help prevent spam and folks who aren't educators from being a distraction to open conversation.
A few specific chats