How much space are you looking at using?
I would look at Adaptec and 3ware raid cards. I haven't tried it but my understanding is you can use SATA drives on a SAS card. If this is true I would really think about using an Adaptec SAS card. This way you can get a card with a 512 MB of ram used as cache and a battery backup. This way you can enable write-cashing on the controller. At work we are using the Adaptec 4805SAS Contoller with 6 146GB Seagate Cheetah's in raid 10. This is crazy fast but low on storage space.

At home I'm using linux software raid5 with 5 320GB Seagate drives on an Athlon 64 X2 4000+ 2.1GHz 65W cpu. I even have it clocked down to 1 GHz using cpufreq and I still get 50+ MB/s when copying data to/from it over the Gigabit network.