Your biggest fan

While not technically transparent, the Dyson Air Multipllier's design is as close to that as possible. I actually have one on my desk, and pretty much everyone HAS to pass their hand through the opening to see if it's REALLY empty (and it is!)
Quite awesome tech, if I've ever seen one...

http://www.dyson.com/fans/desk/am01-10-range/am01-desk-fan-10-white-sil.aspx