Engadget has a post on a interesting Raid1 solution. IO Data Device has a hardware raid that fits 2 2.5 inch hard drives and a Raid controller into a standard 3.5" drive bay. Since this is a hardware based solution, it should work on any hardware and OS that supports IDE drives.
They are pretty expensive: 40, 60, and 80GB models are around $800 USD, $1000 USD, and $1300 USD respectively. Maybe this makes sense for a computer case that has only one drive bay.