Check out areca. The driver is in tree (writen by areca). And it looks like they are actively supporting linux.
They have drivers for RHEL 4 update 3 among many others for their PCIe RAID cards that I looked at.
There was some nice performance comparison betwean linux compatible sata raid cards and areca performed really well. If my memory serves me well it was significantly faster then 3ware. Can't find the url now :(. So i have no arguments to support it now. But certainly areca it's worth a try.
Maybe I will check them out. I've been looking for some PCIe solution for some time and they have great Linux support from the looks of it.