Got a Kill-A-Watt and measured idle power draw of several different types of hardware for general comparison. Looks like I need to replace my current setup before I spend too much on additional electricity usage.
Initial setup
Case: eMachines micro-ATX mini tower
Motherboard: Supermicro PDSBM-LN2+
CPU: Intel Xeon 3060
PSU: Enermax EG465P-VE 460W
Disk: Western Digital 80GB HDD
NICs: Dual onboard Intel 82573L WAN/LAN, Intel Pro/100 PCI for WiFi AP
Current setup same as initial except
PSU: Antec VP450 450W
Test setup 1 same as initial except
Case: ABMX rackmount 1U
PSU: Ablecom 520W 1U
NICs: Intel Pro/1000 MT PCI-X in PCI slot
Test setup 2
Case: generic ATX tower
Motherboard: Supermicro C2SEA
CPU: Intel Q8300
PSU: Antec Neopower 650 Blue 650W
Disk: Seagate 7200.12 500GB HDD
NICs: Onboard Realtek RTL8111C for LAN1, Intel Pro/1000 PT x2 for WAN1/WAN2, Intel Pro/1000 CT for LAN2
Idle power draw
Initial setup: 70W
Current setup: 61W
Test setup 1: 69W
Test setup 2: 54W
and just for grins
Dell Optiplex 980/i3-530/pfsense: 36W
Dell Optiplex 980/i3-530/Win7: 34W
HP 8200 Elite/i5-2500/Win7: 24W
HP 8200 Elite SFF/i5-2400/Win7: 25W