I've seen a couple of "genuine" and "original" products on ebay, which are most probably counterfeit. Most notable are the Hoya filters and Canon batteries, whose price tags are at about 15-50 percent of the retail price. (I'm not talking about third-party products here, I'm talking about falsely branded stuff.)
Googling suggests that they indeed are counterfeit, but it does take some time to find out, and the information is scattered all over the interwebs.
I know that a question asking for a list of fake products is not exactly conforming to the Q+A format, but would it be appropriate as a community wiki?
Related: Would splitting the list into separate questions, such as "Is this battery I found on ebay genuine?", be considered too localized?