The only black/white bad guys, are the people who are set up as the bad guys from the get go. Mehrunes Dagon and the Mythic Dawn in Oblivion, for example. Nothing these guys do, is good. There is that one guy you meet in Paradise that seems ok, but I wouldn't count him as part of the cult.
Besides that, the only other "bad guys" are just people who are dicks. This may be high elves, the Dominion, the Imperials, or Ulfrid, it is up to you. The ES games are good at throwing in moral choice, and--in Skyrim especially--the people you thought were the bad guys, may not seem so bad after all.