Phenom x4 965
any odd you want
500GB caviar blue
windows 7 64 bit
I'm sure it is over your budget, but you really won't get much for $650. I'm sure you need peripherals too.
In general I wouldn't go with AMD CPU. They lack in performance compared to Intel and AMD's efficiency is waaaaay of.
Intel's B75 chipset is a good cheap option if you don't plan to OC the CPU (the same performance as Z77). GPU and RAM OC is still possible though.
I have the above components so I know what I'm talking about. My PC runs cool and silent - CPU max temp during 4x 100% load is around 70°C, GPU max temp during 100% load is around 69°C (fan is set to 40% so its completely silent). The only thing I hear is the main fan which is only audible if your room is silent.