Power Mac G5 Quad SSD Recommendations

Can anyone recommend a make of SSD drive that will work in my G5 Quad. I have tries a Kingston and a Crucial (both SATA III) and neither were seen by Disk Utility.

My HDD set-up is as follows:

Slot A. 500Gb Seagate HDD running 10.5.8

Slot B. the Kingston SATA III and Crucial SATA III are not seen by Disk Utility.

No matter what I try I can't get the SSD's to be seen, I think I need a drive that is SATA II but which make?