CPU (Core 2 Duo)

Used or new CPU stock whole sales:
Anyway, some general guidelines:
- Get a 65nm (or lower, though 45nm parts are not yet available) technology based CPU, since the smaller the manufacturing tech, the lower the power consumption (for equivalent parts ONLY, of course);
- Get a CPU with variable voltage input (I think CnQ always had that, and C1E Intel parts have it too)
- If available, get a low-wattage CPU, since those are made with power consumption in mind.
- Use software to control your CPU speed and voltage, so you can get the most out of it.

That said, here it goes:
Intel "Power Saving CPU list"
- 600 and 900 series, for those of you who can't get Core-based parts because of motherboard incompatibility. They all have EIST (except 62x, 915 and 920), and some also have C1E. Preferred over the 500 and 800 series, because they are 65nm parts (500 and 800 are 90nm);
- 65nm 300 series Cellys, which can be recognized because they all have 512KB of on-board L2 cache, instead of 256KB from 90nm Cellys;
- ANYTHING Core-based, except maybe Extreme Edition and Quad-Core CPUs, is better than Pentium 4s or Pentium Ds, so these would be the way to go if you want low consumption (and increased performance too over P4s, but that's another theme), but even so, the best ones for power consumption are 400 series Cellys, E21xx Pentium Dual Cores and E4xxx Core 2 Duos. M0 stepping ones (you have to check, but E2180 and E4500 have ONLY M0 steppings) are better on idle power consumption, but even L2 ones (everything else in these series, and some E6300 and E6400) are good at that.