What are some websites like Flickr.com?

I'm trying to create a website similar to this: popurls.com

Popurls.com automatically lists popular things of the day, and Flickr seems to be it's source for photos.

I want to add this kind of feature on mine

so here is the question, Do you know any other photo sharing or any kind of service that can be helpful for my plan? I'd like to give the visitors some variety. so I need more sources than just Flickr for the photos

Any ideas?

Thanks, :)