Serial ATA. Particularly if, as SAN_guy eluded on SR, bridged U320 SCSI to SATA enclosures become available.
Floppy replacements, if anyone is listening to me (CF, dammit!)
Anything that improves PC I/O (PCI X, HyperTransport, whatever).
A sound card with native support for DPLII.
Smallish...