Cleric's Challenge (Download)
Pommeville is a sleepy little town that seems like a good place to stay for the night. That is, until the town's dead rise Pommeville unless someone can find a way to comfort the restless dead. A lone, player character cleric will have to be clever, courageous, and more than a little lucky to solve the mystery and save Pommeville from the mindless zombies that threaten it!
This adventure is available from SVGames for 5 bucks. I've actually not run or played this one, but the Wizard's Challenge II and Thief's Challenge II were both cool.
I really like the idea of single-player modules. We've often had a hard time keeping a gaming group for more than a few months, for a number of reasons, so it's often just my wife and me. Adventure design for just one character can be a real challenge, but it's very rewarding, too. That one player can always be the star and gameplay moves much faster with two people at the table than with five+. Good luck!