New pc: AM2, AM2+ or AM3

forget dual cores... thise days it just isnt the way to go... they have no future... so forget the athlon x2
then forget first generation phenoms... they arent that bad for the money... but in the end buying an AM3 system today is just a better choise for the future... new Cpu's comming, DDR3, just a lot more upgradability...

in the athlon x4 and the phenom II x4 it depends on what you need your computer for... if you dont need a lot processing power or are on a tight budget you should go to the athlon x4, but if you do some gaming or just think that you might need the extra horse power go for the phenom =)
on the board side take a look at the GA-MA790FXT-UD5P from gigabyte... i have one and its a superb motherboard full with nice features  

AM3 and DDR3
Don't waste your money on AM2/AM2+ and DDR2 memory.

Get a Phenom II X4 (AM3).
X4 955 BE is 125W TDP
X4 965 BE is 140W TDP with minimal gains over the X4 955

The original Phenom are pointless, they were good for their price until Athlon II X4 was released. Since DDR3 and DDR2 ram cost similar now, and the boards for the 2 are similar, you should just go with an AM3 system. It'll give the best performance and be the most future proof upgrade path.

dual cores are the way to go if you're on a budget.....but this may no longer be true with the athalon IIx4

Yeah, I love the Athlon II X4, that CPU is tearing up the market.  

Hard to buy a dual core when you can get another 2 cores for so damn cheap. That CPU could very well make quad core the 'norm'.

+1 Phenom II 955

New build? Today, AM3 and quad core is what you should be thinking if you are going with an AMD build. Forget dual cores, forget about AM2, and AM2+.

If you're looking for a budget CPU, then the Athlon X4 620 or 630 is a good choice. It's basically the same as a Phenom II without the extra L3 cache. The Phenom II will scale better when overclocked otherwise, it's pretty much the same. I believe they are actually Phenom II rejects re-badged as Athlon X4, just like how the Phenom II X3 and X2 are just rejects of Phenom II X4.

Depending upon your computing activity there is nothing wrong with a dual core. If you are in the USA here is a Phenom X2 545 / Asus 790X Evo AM3 combo for $175 AR.

The new line of X2/X4 Athlon IIs are not Phenom II rejects --- they are a new die

Hi! Thanks for your help. I will buy an AM3 socket. I will choose between the phenom x4 and the athlon II, depending the final cost  
I asked about AM2+ because someone said that it has the performance near AM3 and it's cheaper depending the store.

Have a nice day.

if you are cost sensitive you should probably just check out the athlon ii x4 620 and the phenom ii x4 945... the 945 should be around doble the price of the 620 a little less, you wont get almost twice the performance, but it should be a noticeable diference so you might wanna invest in it since its better to have and not need then need and not have =)

Or could look into a 720 BE for a balance of the 2.