Pc-Engine Darius Alpha
Boxed but not complete, this is one of the rarest Hu-Cards ever published. You could only get a copy of this hardcore shoot-em-up by buying Darius Plus and Super Darius and then mailing coupons to the publisher. 800 copies were made available, and names were drawn from those who mailed their info in. Some copies of the game were also given away as prizes by PC Engine Gekken and Marakatsu magazines.
Loose it fetches around $300 and has gone for up to $1400 complete.