The Antec EA380 Earthwatts or Neo ECO 400,power supplies, whichever is on sale.
Sound is a matter of what you want, Realtech 892 is ok, 889 is better ( best chip found on a motherboard, I believe). the Asus sound cards get a lot of raves starting with the 5.1 DG, how much do you want to spend.
There are four schools of thought concerning HTPC.
The AMD E-350 is a low power dual core improved atom. Does alright to a point
AMD A-series some like the dual core low end 3300/3400 and some insist on the 3650 or 3850 quad cores. Excellent perhaps too much graphics power at the cost of CPU power.
The A75 motherboards seem to be the weapon of choice, the A55 is less without costing much less.
An A75 mb and either dual or quad chips have lots of happy converts.
The Intel club feels that enjoying Sandy Bridge CPU power is the answer, in four variations , H61 motherboard/ G620 Pentium chip ( use on chip graphics or add video card), same with I3 2100 or 2105 (HD2000 or HD3000 graphics).
Or use H67 motherboard instead of H61.
My personal favorite would be an H67 motherboard with one of the SB chips just because you are tying an Operating system to the motherboard.
The AMD 3850 is a convincing arguement except crossfire and scaling are not yet refined. Probably won't matter in an HTPC rig.
Dark horse would be AMD Athlon II X2 255 dual core on 880 motherboard with GT430/440 or HD 5570 OR 5670 VIDEO CARD.
4 GB 1333 Value Ram is considered fine, most people use 8 GB anyway.
Case depends on desired appearance and built in or add on remote control.Smaller generally costs more.