I've lately grown partial to USB interfaces--but not rolled on my
own, but rather using those little USB modules that plug into a 32-
pin DIP socket and give you 8 bits of I/O with send and receive
FIFOs. They're treated as generic communications devices, so there
are no drivers to write on the host side. The big thing to be
careful of is the transfer mode. Single-byte transfer on *any*
generation of USB is very very slow. OTOH, burst/block transfers can
be nice and speedy. Unlike SCSI, USB really *is* plug-and-play.
Cables are easy to come by and you can leech power from the host if
your device doesn't draw too much. All in all, not a bad solution.
SCSI, while simple on the host end (almost any platform has some sort
of "pass through capability", is more of a problem on the device end.
I'm not aware of any generic "plug it into a DIP socket" SCSI module,
which means that you've got that layer to work out and debug.
FWIW,
Chuck