sorry but if you want a stackable Mini HDD there is only one option worth looking at: newertech's miniStack. comes in empty case for $75-80 or with a drive pre-installed + drive utilities. You can get a 500GB for $295. The iOmega is a rip-off as it is overpriced and the buffer is only 2MB. The LaCie though I like their products is not attractive. Go to
www.macsales.com and choose Mac Mini upgrades from the drop down.
The 250 is $160, the 320 is $190, the 400 is $270 and the 500 is $295 and they all have 7200 RPM 16MB buffer Seagate Barracude drives. They can be used in Firewire or USB and have lots of extra ports and can be set to switch on with the Mini.