Dear Jeff
you shall find a good overview at Dantz knowledge base:
http://www.dantz.com/en/support/kbase.d ... y&id=27381
The article does include a SCSI trouble-shooting guide.
You will find similar articles at Apple's website, of course:
http://search.info.apple.com/?search=Go ... rd=&q=SCSI
Be sure to read Adaptec's compatibility notes if you consider upgrading to Panther at any point:
http://adaptec-tic.adaptec.com/cgi-bin/ ... aqid=11052
A manufacturer left out in Dantz' list is Acard, who do produce SCSI controllers (especially the 6712TUM and the 67160M) which our testing center had no troubles with, even under Panther and on G5 macs:
http://www.acard.com/eng/
On their starting site there's a G5 compatibility list, too.
You possibly might also want to consider firewire-to-SCSI converters, like the Belkin FSU451 or the Ratoc FR1SX.