Best CPU under $175

Phenom II x3-x4 if you get a x3 it has the possibility of unlocking the 4th core without problem I did with mine. Make sure to get a black edition processor so the multiplier is unlocked for max OCing i recommend the AMD phenom II x3 720 BE

Hmmm... tough choice.

The $400 for all three pretty much throws i7 option out. (i7 = $290; good X58 board - ~$190+ ).

This is probably one of the good/best deals for Phenom 2:
http://www.newegg.com/Product/ComboDealDetails.aspx?Ite...
Phenom II X4 810 + Gigabyte 790X board
$295

On the Intel side:
P45-UD3P ($115 after MIR) + Q6600 ($214) or E8400($165)
Total: $329 (w Q6600) or $280 (w E8400)

The price difference all comes down to the RAM. Choosing between the Phenom II and the Intel Q6600/E8400 is up to you.

Imo, considering that LGA775 is EOL I would get the Phenom 2. Or if you are on a very tight budget P45-UD3P + E8400.

Best bang for buck (imo)
P45-UD3L($93) + E5200($70) or E8400($165)
Total: $163 (w E5200).

edit:

All prices are Newegg prices.

Phenom II X3 720 Black Edition. $150, unlocked multi, great OCing, extra core over duals, can use AM2+ or AM3, DDR2 or DDR3.

Mehh...I like Core 2 Duo E8500. It is solid, superb overclocking, 6MB of cache, 3GHz (about) factory clock. If you are not that much of a gamer, I would get a Q8200. 4MB of cache, 2.8GHz ( i think), and quad core respectively.

^^ E8500 is good i guess, but for a lower price you can get the extra core and equal overclocking capabilities with the 720.

As for the Q8200, both the 720 and the 940 walk all over it.

True that.

I'd take the 720 and a decent mobo. Personally, I'd grab something like an Asus M4A78-E, but if you want to try and unlock the fourth core, you'd want something else.