There are a number of eSATA PCI cards that are OS X compatible. Some are name brand (and therefore much more expensive) while others are generic but are based on the same chipset and use the same driver as the name brand cards. One of the most popular PCI eSATA chipsets goes by device ID 3124. I got a generic card that listed that device ID, so I searched around until I found the name brand vendor, Silicon Image, and the
product page for the name brand card. Then it was easy enough to find the driver that would drive my generic card.
As for SATA versus SATA II, don't worry about that largely meaningless distinction - all SATA drives are generally backward and forward compatible.