ruleslawyer
Registered User
There's a pretty awesome (but rather distinctive, so it might be hard to reuse) thieves' guild in Dungeon #19, in the adventure House of Cards. Dragon 115 has some excellent tools for building and running thieves' guilds, though IIRC there's no sample thieves' guild therein. For a lair or the like, "The Assassins' Run" is probably the best option.