Digit-Life posted a guide about choosing a motherboard for a middle-end machine

To uncover the full potential of the newest quad-core AMD Phenom X4 and FX processors one should install these into Socket AM2+ boards based on AMD 790FX, 790X and 770 chipsets. However, the new processors can be installed into Socket AM2 boards as well. Actually, of all possible combinations only installing Socket AM2/AM2+ processors into Socket AM3 boards is not possible.

Choosing a Motherboard for a Middle-End Machine (Socket AM2)