While not strickly a 'Mac', my Apple Network Server 500/200 with two DEC Storageworks RAID arrays connected was the most power hungry machine. In fact I had to retire it because of what it was costing to run!

Unfortunately, I chose to replace it with a G4 Xserve with an internal RAID arrangement (nothing too fancy), and recently calculated that it consumes around 10% of my house power bill (compared to my Cube which seems to take about 1%).

Kind regards,

Macdownunder