This was an HTPC build for
Steam Streaming and Light/Medium Gaming.
The two "free" hard drives were leftovers from upgrading my Laptop (ASUS Zenbook UX32VD) to a 500GB SSD and my PlayStation 4 to a 2TB HDD. I have them arranged in a RAID 0 array since this computer won't have critical data on it.
For those curious, yes my laptop and PS4 had EXACTLY the same hard drive. Go figure. https://www.ifixit.com/Teardown/Asus+Zenbook+UX32VD+Teardown/10120#s37402 https://www.ifixit.com/Teardown/PlayStation+4+Teardown/19493#s54777
The GTX 560 Ti is also a leftover from upgrading an older PC to a GTX 960. It runs really hot when under load, so I might look at upgrading it in the near future.
Overall, it was a pretty fun build considering the space constraints and the final form factor is really awesome. It's cool to see it fit right under my TV.
UPDATE 12/5/2015: I upgraded the old GPU (EVGA GTX 560 ti) to a EVGA GeForce GTX 960 2GB SuperSC
UPDATE 9/2/2016: I upgraded the old GPU (EVGA GeForce GTX 960 2GB SuperSC) to a ASUS GeForce GTX 1060 TURBO. After this upgrade, this little beast is clearly a Gaming PC. I can play any game I want on it.