Jeff Rients has posted a OD&D module, Under Xylarthen's Tower, over at Jeff's Gameblog in this post: my module: now less crappy.
Under Xylarthen's Tower is a very nice 6 level old school dungeon in a pdf file. It even has a dragon's lair. Jeff has some interesting takes on monsters as well. That's one of the nice things about OD&D, the monster descriptions were very sketchy -- especially on what the monster looks like -- which gives a dungeon master a lot of room to customize things for his or her world.