An asymmetrical airplane, the Blohm Voss BV 141. Despite it’s appearance, it was actually perfectly stable- the asymmetry of the design was balanced out by the torque of the single engine.
Sounds like the electronic version of homeopathy- it “learns” what it’s supposed to do! 
The Cat Genie, a $300 cat toilet. Although, I have to admit, cat owners seem to like it, and anything that allows you to not handle cat waste has to be a good thing.
The beer hat. Do people actually buy these, other than as a gag?
Blast! Pykrete was already mentioned.