Blu-Ray and Media Center (XBMC) capabilities
USB 3.0 (for my external HDD with all my movies)
Light gaming capabilities (Steam's Big Picture mode, emulators for my old consoles)
Aftermarket cooling of some sort so it's quieter
Modular PSU for ease of installation
No overly-bright LEDs
Small footprint to fit in my entertainment center easily
SSD for OS
Windows 8 (willing to use Windows 7 if necessary)
What I'm trying to decide is whether I get an Intel processor and cannibalize my main PC's GPU (MSI Twin Frozr II 560 ti 2GB) for graphics and use this as impetus for upgrading to a 7950, or whether I get an APU and a 7750/7770 with the understanding that I will upgrade to a Kaveri-based APU when they are released.
My budget is somewhere in the neck of $500. I already have 8GB of 1333 RAM and a 500gb internal drive for storage. I have no real preference between mATX and ITX, though I think I would prefer ITX. Networking isn't a problem, my house is wired and I've got a free ethernet drop for the PC.