http://www.vwbpe.org/

This conference is free. According to the website, the first year, over 1500 unique avatars attended and the second year, over 3800 unique avatars attended this conference.
This year there will be 192 presentations and 500 presenters with an expectation of 5000 attendees. Check out the conference website. I plan to attend for the first time and will post a blog about the experience.