One of the most famous of the free photos sites and with good reason. The quality is stunning and the selection is broad. Over 200,000 high-resolution images, with thousands more added every day.
Not as consistently high quality as Unsplash, but over a million images and videos uploaded by thousands of Pixabay users. Interestingly, they crowd source quality control to help keep the inflow to a high standard. Looking through the declined photos stream is a fascinating glimpse into what people try to release into the public domain.
A newer entrant in the wave of "not like traditional stock" photography. A small but growing collection of photos with a curatorial leaning toward normal people doing normal things. Signup required.