-D- wrote:
AND some clockport sound cards 
That's right, I remember the Melody 1200 had a cool plate that fitted four audio connectors in that space.
I've also seen PS/2 mouse adapters and external keyboard adapters fit into that space. I think the two most common uses though are for external scsi port from a trapdoor accelerator or a DB25 fast serial port connector (hypercom, silversurfer, twister, etc.).