I've decided to split this issue into two parts... First: CPUs.
People like to complain... A LOT... that modern CPUs are too hot. While I agree to some extent, the fact is, you just need to be more knowledgable, and you can still get very high-end CPUs with very low power requirements.
Because people have varying needs, I've included processors of many different speeds, and varying power requirements. The only rule is that they have to stand-out as significantly lower power than similar processors.
I include both Intel and AMD chips. I do not include VIA processors, because their performance is quite terrible, and their power requirements not all that low. And most importantly, I am listing desktop chips only, not mobile processors.
Proc Model Max
PIII-800 (6-B-x) 10.63W
Athlon 6-8-1 XP-1600+ 48.5W
Opteron-140 (1.15V) 30W
Athlon 64 (1.0GHz 1.1V) 22W
Sempron (1.0GHz 1.1V) 20W
Athlon 64 FX (1.2GHz) 25W
Xeon-1.6G LV 30W
Athlon 6-A-0 XP-2000+ 60.3W
Sempron 6-A-0 3000+ 62W
BTW, that was a very nice looking table before Slashcode chewed it up, and stripped important info for no particular reason.
Anyhow, processor selection is only about 1/3 of the battle. The even more important issues is power draw, and power management of your motherboard. Unfortunately, neither one is publicly documented, nor are the manufacturers willing to release ANY information at all when I requested that they do so. So, it's very tricky.