I'm tired of moral ambiguity. I'm totally ready to go back to cut and dried good and evil. And yes, I'd love to see some evil guilds. Of evil paths to finishing them. The holy grail is an evil version of the main quest, but that will likely only be doable through mods.
Read the quest line for the Mages Guild and Fighters Guild in Morrowind.
Hell, everyone, just read the quest lines for every organization in Morrowind.
An example, the Fighters Guild is split between those who are in the pockets of the dunmer crime syndicate, and those who are not. The guys who are corrupt tend to give quests that involve you shaking down businesses and people to pay up protection money, or find information about the Theives Guild. The non-corrupt guys tend to do normal jobs, like deliver booze to a mine deep in a remote area, clear a cave of dangerous pests, assist other guilds (like helping the temple clear a necromancer den), and, though some wiggling around, help the Thieves Guild.
Or the mages guild. You someone to win a bet, work with a completely inept guild master, remove the inept guild master from office or share it, kill off the Telvanni, not do down the route to kill off the Telvanni, assist someone travelling to get his notes (but it doesn't matter is said person dies), collect dues from delinquent members and kill them if they refuse, etc.
The Telvanni were very amoral, but not evil.
Redoran is high on honor, yet are corrupt and tend to act like children when dealing with other people.