Building an HTPC:

The H55/H57 chipsets and Intel i3/i5's are perfect for HTPC use as long as they fit your budget.

I can't find that model of motherboard on Gigabyte's website. Did you mean GA-H55-UD3H? If so, ensure that you really want an ATX rather than micro-ATX for your set up.

Also, in my opinion the 661 is not worth the extra money for the slight increase on the GPU clock. An i3 or the i5 650 is perfectly good for HTPC use.

I'll probably get ripped for this, but the ATI chipsets from AMD are about the best you can get for an HTPC. Check out the 785G boards (they pass sound via the HDMI as well).