This may be common knowlegde but I don't see it posted here so I thought I'd share my limited flashing knowledge. ; )
As mentioned in this article from xlr8yourmac:
A cheap PC Adaptec 39160 dual channel U160 SCSI card can be VERY easely flashed to work on a Mac.
1. Get a PC Adaptec 39160
2. Download Adaptec OS 9 flash utility and most recent 39160 firmware from adaptec.com
3. Install card in Mac
4. Boot into OS 9
5. Run flash utility
6. Use your new card!
ATTO has faster cards now (and it looks like Adaptec has no plans to extend their Mac line) but if you need SCSI on your Mac this is a cheap way to get it. They're on Ebay for under $50 and there's so many pulled from PC servers that you can probably get freebies from your PC-using buds. So far its worked fine for me in 10.3 and 9.2.2.