I just created my second website for hdri skies only (after hdrmaps.com).
There are 82 free hdri skies at the moment, but I will upload more soon. All of them are free but registration is required. No worries about spam - I’ve never sent any spam from hdrmaps.com.
It will always be free so no worries - it’s not time limited, but as a reward you can share link to hdri-skies.com on your blog or on social media. Click on image to go to hdri-skies.com