Hrm. So maybe the nslu2 with the spun-down drives is still the best answer, if power (or temp!) is your biggest concern.
You said it. I just measured 5 (FIVE!) watts in standby with my slug and 320GB Western Digital drive (also unslung to a stick). That comes to 11VA if I also take the power factor into account caused by the switched mode power bricks. Active, while doing a scan to build the database, its just about 9 watts (and maybe 20VA).