I really like the free photo site Unsplash, I hardly use stock image sites such as iStock or Shutterstock anymore. As a pro with paying clients, the prices of the stock images are not really a concern in the overall budget of a presentation design project, it is simply the dilution of quality of these big stock photo sites with cheesy images.
But worryingly, I see the first “stock images” pop up on Unsplash as well, I hope they will continue to curate their uploads carefully, or maybe add a “stock image alert” warning button on a photo.