If you are experienced with computer hardware then this review may seem pointless as I shall be basing it around the less enthusiastic end user.
If you are looking for a processor to fit an AMD motherboard, the Phenom X4 955 Black Edition is perhaps the best performance for value you can buy at the time of writing this review. AMD do provide 6 core Phenom processors but unless you use very high demanding video editing software I feel it will be waste. This processor is designed for a gaming enthusiast since games developers are just starting to make games that use quad core processors.
But why not buy a quad core phenom with a higher clock speed (xxGHz)?
Well, the 'Black Edition' AMD processors come with an 'unlocked multiplier'. This in simple terms means you can make the clock speed just as much as it's bigger brothers, while keeping the price down. And for the less informed, AMD have made it easier by providing AMD Overdrive for download on their website. This program has both simple and advanced controls to supplement everyone.
A little research will show that the 955 BE will work on AM2+, AM3 and AM3+ motherboards (there are limitations which will be explained on your motherboard website). This means that even if you decide to upgrade your motherboard (I went from AGP to PCI-E) you can still keep the same processor, saving money.
Typing the processor name into google will provide a plethora of top reviews and comments from all over the world about this diverse and solid processor. The stock cooling is efficient, I have found it possible to overclock to 3.6-3.8 GHz without changing the voltage (I don't like changing the voltage, but it can yield amazing results). I have friends that have the 955 BE at 4GHz+.
Incase anyone was wandering, the 955 BE gives a 7.3 processor windows performance index rating out of a maximum 7.9 at stock clock speeds and voltage (although I feel this requires some sort of update for the next generation).
I urge anyone looking for an AMD processor to buy this, as it represents real value for money without skimping on performance.
EDIT: I have my Phenom II x4 955 BE running at 4GHz now. The voltage is set to 'auto' (which isn't ideal for overclocking as the motherboard can provide unnecessarily high voltage which leads to more heat). It seems stable after running various 'stress test' applications, but I feel the stock cooler does not provide adequate cooling for overclocking of this sort.
The fan is noisy when it is anywhere near 70%+ spin. I have noticed that after several weeks the heatsink and fan seem very clean compared to others after the same timescale (The intake on the side of my case has no filter and the black colour is coated in dust. Very amateur of me, but it is on my list).