Home Network Data Storage Device

It happened again- a machine on my home network died. Taking with it tons of data. It's mostly backed up. No huge loss. But I finally think it's time to get some sort of network raid disk. A unified place to safely store data accessible to the numerous machines on my home lan. So now I pose to Slashdot readers- what are your recommendations? I'm looking for something with RAID and SMB sharing. At least a quarter TB, probably a half, but with some room to grow. What have you used? What works? What fails?