This section is like a nursery section where links are grown before transplanting out to their own sections, where they would be put into context. Links here have caught my fancy. I leave it to others to attempt to maintain comprehensive lists. In my experience, the major search engines throw up most of what's available.
Sites also disappear without warning.
It is very general however. The ancient Celts can't be treated as an homogenous group. They share aspects of culture, but they are not a unit. The T r's focus is pre-Celtic and Celtic Ireland, which would be up to the Iron Age. Given the lack of physical evidence available, a picture of society in those times can only be formed from a combination of archaelogical evidence and mythology.