If you have a bit of time and want to see what is out there in the land of OER this isn’t a bad list to start with.
At a practical level we still need topic specific gateways that pull from all these sites. Until we do, finding relevant resources is going to be inconvenient for time poor academics.
http://campustechnology.com/Articles/2014/07/02/16-OER-Sites-Every-Educator-Should-Know.aspx?Page=1