Free to use image sites are all important to website designers and below you will find quite a few sources for free images. The order is merely a matter of my opinion alone. Since we are dealing with photos, and we all know that beauty is in the eye of the beholder, I encourage you to browse through these and find the sites that you like the most. Ordering them to my preference is merely a matter of my own personal convenience.
I maintain some very large HDDs on two PCs and have many of my favorites images downloaded because it is simpler than trying to remember what I saw where, or finding them again. I would encourage you to do the same if you have the resources. This will cut back on frustration and perhaps even very small degrees of insanity.
Having said all this I must caution you that not all images on all these sites are "free to use", or they may be "free use" but require some sort of attribution. Be sure to check to see what the requirements are for the photos and sites that you wish to use before you use them! Reverse searches of photos is very simple these days and none of us wants that "cease and desist" email, or worse.
Were I not presently redesigning my site, with customers and life keeping me too busy to finish it off, I would comment on each site and tell you a little bit about each one. I will do this where it is easy for me. Clicking on either the title or the image will take you to that site.
Enjoy and stay legal, and don't forget to size and optimize your images. Some of these images are almost big enough to paste onto a billboard and slowing your site down to a crawl where loading is concerned is one major taboo. If you need a site to trim and shrink photos online I highly recommend befunky.com It has a nice comfortable interface and some very good options to choose from.
This one of my favorites, as you can tell by it's placement at the top of this list. I have built whole projects from this site.
Another favorite of mine.
At this point ordering is becoming irrelevant to my tastes. I will just be listing them in the order I come to them.
No, I didn't mess up the screenshot, that's really how the site looks. But they have free photos.
This one is a newcomer to the list. At first glance it looks as though it leans heavily of photos that have had effects added through Photoshop or something like it.
Despite the name, this site offers a lot more than just images of barns.
Just bumped into this one. Only PNGs.
This resource/site is for videos. Some of the others have videos as well but this one seems to be solely videos.