There's also the i-RAM ( http://techreport.com/reviews/2006q1/gigabyte-iram/index.x?pg=1 ), a battery-backed RAM disk. My employer uses it for an app where disks simply couldn't deliver the latency we needed, and yet it had to be fault tolerant enough to survive a power failure.

Edit: wow, totally did not see Sam_odio's original post, linking to exactly the same product. Oops. And yCombinator doesn't allow us to delete comments...