For the use you describe, look at an i3 with the new intel on-chip graphics. You could almost halve the cost.
Last Fall I built an HTPC just to use up some spare parts. Used an intel mobo (H55 i think) and i3-540. Slapped in a BD burner and just plugged it into an HDMI port on my receiver.
Didn't expect much, but have been Astonished how well it works. Except for the burner, max power is 34 watts for the whole box. Encodes/decodes great, streams HD vid and bitstream audio with no tweaks. Kids love it and we hardly ever turn the cable box on now.
