I've found from my experience that silverstone makes good cases. An example is
this one. The more you pay, the better the case will be, but that one is a pretty good low-end starter case.
Silverstone also makes good
power supplies. Though I don't use them for desktops, their PSUs tend to be quieter than others, even under full load. However, because of that quiet, they also tend to heat up more.
Though I usually go with Intel for my builds, for my HTPC I've gone with AMD twice, and Intel once. AMD processors seem to require less in terms of space, and function better in smaller builds in my experience.
I used a HDD in my first two builds- my last build was my first with SSD, and I can say that it has made it more responsive.
My last one was also the first time I went with onboard video instead of low profile. I'm definitely going with Low profile again when I build another; I see the difference on web based video, though not on video files strangely enough. Netflix and Youtube aren't working as well on the onboard video, though playing video files from my NAS works fine.
And I've just been using Windows Media Center for the software (on Windows 7). I've tried a few different things... from media monkey to a couple of other things (I'd have to look them up). I haven't tried a dedicated OS solution though, so I can't comment on those.
As far as controlling it, I have always used logitech solutions before... but I just used a
low end rosewill remote this time, and it works fine. I paired that up with an
iogear keyboard with built in trackball, and I've been set as far as controlling it.
Hope that helps... let me know if you have any other questions.