You might want to look at the Antec ISK-300-150.
Antec makes reliable psu's and this case was reviewed well by www.silentpcreview.com.
It can lay flat or upright so it should fit under that 5" shelf.http://www.newegg.com/Product/Product.aspx?Item=N82E16811129080
It has a 150w psu. That is plenty if you will use a G9650 clarkdale cpu or similar.
just because I'm using a HTPC sized case doesn't mean I'm going with an atom-sized processor. I'm planimg a micro-ATX build with a Athlon II X3 processor and an ATI 5570 graphics card. An ITX board is possible, but more expensive, thre heaoest DDR3 ITX board is $125, while a micro atx AMD DDR3 board is about $65
with that cpu and gpu, 150W is probably too little. 250-300 will be needed