Well...I guess kind of all of the above, since I mainly want to see what is out there. IR receiver, volume knob, and VFD are not requirements necessarily; I feel like I haven't seen or heard about a VFD yet that was well-integrated into an HTPC case.
In terms of form factor, full-size or slim design is ideal, as it at least be able to sit in the company of other AV equipment. If it's a nice looking horizontal case, that may be just fine, I suppose.
The lines I'm most familiar with are Silverstone's and Lian Li's, and now Thermaltake's (that Mozart you mentioned is kinda hiddy, isn't it - hard to imagine that sitting in a living room!). Any other suggestions are welcome!