Maxperson
Morkus from Orkus
1e required it. Spells came to you from your god via intermediaries, except for 7th level spells which were brought personally by the god. In 2e you could get 1st and 2nd level spells by faith alone, regardless of where that faith was placed. The Clerics Handbook(I forget the exact name) mentions philosophies and forces as possible sources of spells.The 3e Forgotten Realms guides said everyone needs to have a deity, or they get sucked into the wall. All clerics, druids, and paladins had deities. But AFAIK that's the only setting in the only edition that ever strictly required it.
Oh, and the 3.5e PHB said that you could be a cleric of a cause or a source of divine power that wasn't a god.