In no particular order:
Bedtime Stories - Ugh. Horrible writing, horrible acting, cheesey special effects. I love children's movies, so don't go "it wasn't target at your age demograph, blah blah blah!"
Shark Boy and Lava Girl - They play this on the Disney Channel constantly. Its awful. Plenty of towards-the-screen motions, so I'm guessing it was originally in 3D.
Dead Alive - Too rediculous to be scary, too gory to be funny. I'm not sure what kind of movie Peter Jackson was trying to make here. In the very last scene, it dawned on me that the whole movie may have been one huge metaphor for a man trying to break out of the teenage mindset and get into the adult world, but that didn't make up for the rest of it.
National Treasure - Hated it.
I can't think of anything else at the moment. I haven't seen a whole lot of truely bad movies.