This self-described "journal of the politics of driving" is a tremendous resource. Photo Enforcement is the author's primary focus.
This site discusses red-light cameras, including their common errors. It's great for anyone fighting a camera ticket, especially in California.
This site features a user-maintained list of red-light cameras and photo radar locations throughout the United States. You can even add to the list.
POI Factory has a free database of camera locations for GPS users. The data is cooperatively maintained and free to active participants on the site.
The NMA opposes the use of photographic devices to issue tickets. Speed cameras encourage artificially low speed limits and revenue-driven enforcement.