go with an am2+ proccessor like the phenom II 940 black edition with an asus m4a78 mobo and then u can always upgrade to am3. cheap aswell just not ddr3.
i was looking at the am3 processors and i have heard some good things but the only problem it that i would have to use ddr3 memory, and i don't really want to switch to ddr3 unless it is really worth it for the am3 processor.