Flickr is a good bet. It's definitely intended for shutterbugs (it's big on albums, collections, tagging and the like), but I use it all the time for the photos I want to preserve and share for the ages. I'm on Flickr Pro so I can't attest to how well the free tier works, but 1TB of free space? That's a lot. I've been using it since 2009 and I've barely made a drop in the bucket.