How to know how much power a server will need – for colocation

I did some stats on this a while ago FWIW, using the handy dandy kill-a-watt..

Typical Developer Dell PC
(2.13 GHz Core 2 Duo, 2 GB RAM, 10k RPM 74 GB main hard drive, 7200 RPM 500 GB data drive, Radeon X1550 video)

Sleep                            1 w
Idle                            80 w
One CPU core fully loaded      108 w
Both CPU cores fully loaded    122 w

Standard Developer Thinkpad T-60 Laptop
(core 2 duo 2.0 GHz, 100GB hdd, ATI X1400 video)

Sleep                            1 w
Idle                            66 w
One CPU core fully loaded       74 w
Both CPU cores fully loaded     82 w

LCDs

Old Dell 19"                    50 w
Ancient, giant 21" NEC          67 w
New Dell 19"                    28 w
New Samsung 19"                 28 w
Apple 23" LCD                   72 w
Samsung 24" LCD                 54 w

It turns out with the LCDs the default brightness level has a lot to do with how much power they draw. I almost immediately turn any LCD I own down to 50% bright, just because my eyes are overwhelmed if I don't...

I'm not sure about servers, but the current thinking in embedded devices is not to bother with steps between low-power and flat-out because the extra time involved will eat your power savings, so basically they run low power until they get any real amount of cpu load at which point they flip over to fastest-possible so they can finish the job and get back to idling at low power.