I've just successfully installed a SYBA SD-SA2PEX-2IR PCI Express SATA II Controller Card http://www.newegg.com/Product/Product.asp?Item=N82E16815124027. It was fully supported in unRAID, v4.0-beta9, uses sata_sil24 module, thanks Tom!
It's based on the Silicon Image 3132 chipset, which supports 2 internal or external SATA II ports. This may not sound exactly like what you want, but 3132-based cards claim to support the new port multiplier technology, as in this http://www.addonics.com/products/host_controller/ad5sapm.asp. Tom says support is still 'experimental', but it seems exciting for the future, to be able to easily add 10 SATA ports (one 3132-based card ($35) and 2 5-in-1 port multiplier cards (2x$85)). I especially like the Addonics cards' no-slot feature, uses any unused slot bracket but no PCI or PCI-E or other slot type, requires a floppy power connection only.
See also this thread http://lime-technology.com/forum/index.php?topic=567.0.
I've only just installed and tested the Syba card, and the speed 'seems' very good, but I can't give you any long-term reliability thoughts.
On the first boot, there were lots of boot errors and unRAID did not start, but after a reboot, it seemed to reconfigure itself and came up perfect. I moved the SATA cable attached to /dev/md2 (my third SATA drive) to the first SATA connector on the Syba card, from the the third motherboard SATA connector. After the installation and the extra reboot, and a re-select of my HD on the Devices page, the unRAID server started up perfectly, not even a parity check required. In other words, I moved a drive to a completely different disk controller, and nothing had to be rebuilt, re-initialized, whatever! Try doing that with most other RAID systems, especially if striped! (I'm very new to unRAID, so my terminology may be wrong.)
I bought this one from Newegg for $25, it's now $35, similar to other comparable cards. Price range for 2-port SATA II cards seems to be about $25 to $40. To get a 4-port card, price jumps to $110 and up and always seems to have RAID. I could not find anything with 4 or more ports that did not also require paying for RAID even if you don't want RAID.
I did install it first on a Windows XP, in order to flash the BIOS to the latest, 7.3.13, from Silicon Image web site.
I just checked and all 3 SATA drives have spun down, that is sooo cool!!! Can't wait to add more drives and the pro version of unRAID.