According to DigiTimes, a company known as CFI, or Chyang Fun Industry, has premiered a hard drive case at Computex that supports up to four 250GB hard drives for a total of 1 TB. The case has a cooling system that CFI claims is capable of keeping the drives at 35oC. The unit also sports USB 2.0 connectivity.
While it may be nice to have a 1 TB external hard drive, the case is quite bulky (click the DigiTimes link above for pictures). Other than that, it looks like a nifty contraption that might be able to stay on the market as long as CFI can continue to update the support for larger and larger hard drives.