Finding a SATA controller for OpenSolaris is a bit more difficult than for Windows or Linux. Having scanned various web sites and mailing list archives I had come to the conclusion that something based on a Silicon Image 3124 or 3132 (SIL 3124/3132) would probably be the best choice. The other thing that proved to be challenging was to find something I could actually buy in Germany. Various models had received good feedback but were seemingly not available here, whereas it seemed easy to get them in the US or UK. So I finally ended up with the Dawicontrol DC-310e (product overview in German), that works with OpenSolaris. (Interestingly, you will probably not find this controller outside of German speaking countries.)
What is nice about the DC-310e is its capability to disable the BIOS by removing a jumper. Most such adapters come with some obscure form of RAID functionality, which is certainly something you want to be careful about. And for ZFS you definitely just want a plain controller without anything else. So for almost all SATA controllers the first thing you need to do is flash their BIOS with a non-RAID version. Although technically not so challenging it is a tedious activity and I was happy not having to do it.
During initial testing of the Dawicontrol DC-310e I witnessed a few situations when my system (running Nexenta 3.0) froze completely under load. This had not happened with the built-in SATA ports. My final approach, or rather workaround, was to only use one of the two ports of the DC-310e and since then I have had no problems. I am still not really sure what the actual root cause was. E.g. I had also changed the PCIe slot because the one used initially did not put a firm grip on the card. Since I stopped working on the issue once I had found a working configuration, it would be unfair to simply blame the controller. The system has been in use for more than six months now without issues.