I have my HTPC in a 2u case. Stock CPU cooler (i3-2100), full size ATX psu, microATX board, low profile gt 430 (no riser), SSD, 2.5" hdd, and a Blu-ray drive all fit fine with no problems. I can actually fit four 3.5 hdds instead of the 2.5" ones and still not have any issues. Though the one thing I'd recommend is getting a modular PSU. I didn't have one on hand and didn't feel like buying one, so there are a lot of wires stuffed under the Blu-ray drive that I'm not using.
Another thing to keep in mind is the sound on these cases. Most of them were made to be in server rooms. So if you're rack is in your theater, you're probably going to have to swap out the stock fans. In my case they sounded like a tornado. My rack is 30 ft from my theater, but I still had to swap the fans out because it was generally annoying.