Nice build!
This is about the same as my htpc.
The processor is very energy efficient.
Your psu is probably over kill as said above. I am using a good Seasonic 400W.
I would consider Western Digital Green (energy efficient) or black (great performer) caviar as hard disk.
Lian-Li Lancool PC-K56WB case is larger than you shuttle XPC, if you want good small case, you can look at nmedia as they are cheaper than Lian-li/silverstone and do very well!
Edit: Your ram doesnt match any qualfied motherboards from g.skill website
G.SKILL-Products
I would suggest you;
Gigabyte GA-MA785GT-UD3H AMD785G ATX AM3 2PCI-E DDR3 Video Sound GLAN CrossFireX HDMI Motherboard
Why using a mATX board when your case is actually ATX? This is not much price difference with your current board and this one support your ram!
Note: The Ati HD 4200 integrated video card in these motherboards is really good. You will be able to play many titles. Maybe not all maxed but, it work quite good!