This machine is only going to be used for ripping, compressing, and hosting my bluray backups. I'm running Ubuntu 13.10 for now using MakeMKV and Handbrake.
CPU: Overkill? Maybe, but this will be transcoding on the fly for anyone who is playing movies via plex. Also, when I get board in a couple years this will have plenty of room for overclocking. I also wanted something that wouldn't have issues with integrated graphics.
Cooler: Pretty standard cooler. I'm still running a little hotter than I would have expected, so I may need to reseat the cooler.
MB: I'm a fan of ASRock and this makes overclocking super easy.
Memory: I don't ever plan on upgrading this so I went for a long term solution. Lots of RAM and reasonably fast. Currently have it overclocked to 2400MHz
Storage: Ubuntu is running off the mSATA card making the machine feel very quick. Raid5 mdadm array with the other four drives.
Case: Love the case. It fits very well into my home theater and the flat front makes for a non-obtrusive addition to the living room. It came with a couple fans that I will probably be replacing soon for something quieter, but the included damping material makes for fairly silent operation.
PSU: On the off chance that I put in a video card I have room to grow with the PSU. Runs silently, I'm not sure the fan has ever needed to turn on, but I like that the fan is there if it's needed.
Optical: Nothing fancy, plays blurays well on VLC with the required libraries.