SLO Bytes Digital Photography Group

Royalty Free Stock Photos

http://deathtothestockphoto.com/ via email once a month.
http://www.imageafter.com/
https://www.pexels.com (under Creative Commons CC0 License)
http://www.freestockphotos.biz/ (various Licenses, need to be careful to use correct ones)
https://www.flickr.com (has a search by license option)