- Wikimedia Commons of course.
- Mav's images. (WT-en) Maveric149 says, "I have a couple hundred images of various national parks and other things in the western part of the United States. Anybody can use them under terms of either the GNU FDL or CC-Att/SA." (see dual licensing for more info on dual-licensed works)
- PD Photo. Several thousand images, all in the public domain. Very nice quality, too.
- OpenPhoto.net. A repository of more than 22,000 photographs available under the Creative Commons Attribution license. (This is compatible with our copyleft, as long as we copy over the attribution, too.)
- Gimp-savvy.com. Public domain photographs from the US Government, arranged and catalogued by volunteers.
- Buzznet has loads of stuff released under its default licence, which is the same as ours.
- BurningWell - a repository for public domain images.
- A minority of Flickr images are under a compatible licence; seek "Creative Commons-licensed content for commercial use, adaptation, modification or building upon" by selecting every one of the "Creative Commons" options on an advanced search. Bots to import these images to Commons include User:Flickr upload bot and User:File Upload Bot. Images with "non-commercial" or "no derivatives" conditions are not usable.
- Geograph Great Britain and Ireland. Based on the Ordnance Survey National Grid, all photos are geotagged, so you can search for a specific location. All photos are licensed as CC-BY-SA. They can be uploaded using Geograph-to-Commons.