Last week I bought (on a local dutch ad site) a trackdisplay for the Amiga 2000. It replaces the LED board and adds a display of 4 digits which show what track on DF0 and DF1 is being read/written. I couldn't find this piece of hardware anywhere on the Internet so I submitted it to the Big Book (should appear there shortly I presume).
Has anyone else ever found a piece of hardware that was previously "unknown" (at least to BBOAH or the Amiga Hardware Database)?