Rework a classic P&P quest from the old days of D&D. Haunted Halls of Eveningstar is nice, but let's face it: old D&D was Blackmoor, Oerth, and Grayhawk.
There is so much material to choose from. I find it hard to believe that at least one of those modules couldn't be reimagined into a set of 2 or 3 quests.