I'm aware of the Z-drive, they even have a 2TB version, but the price makes this drive uninteresting for most users.
There are even faster drives out there with 5GB/s transfer speeds and up to 6TB.
But the RevoDrive X2 are the only ones that are affordable by the majority of consumer Mac Pro users. I don't think that there are much users that can justify a drive that is worth more than the whole computer.