An Illuminating Case Mod
A huge side window like the one on Corsair's Obsidian 900D almost begs for some sort of internal illumination, and ever since the day one of my Christmas trees won an award for being tacky, I cannot past up a lighting challenge.
I opted for a three-foot long LED strip, which I installed by starting at the top-right corner and running it counterclockwise to the lower-left corner. It has an adhesive on the back, and simply sticks to the metal. On the left side, point it towards the enclosure's interior to minimize glare. If you want to do something a little different, you can buy remote-controlled LED strips or multi-color kits with effects. Just make sure they operate at 12 V so you don't need an external power supply.
The video below shows my install with audio control, enabled by CCFLs (cold-cathode fluorescent lamps), available for around $5 and up. To avoid clutter, you can hide the control electronics in one of the unused 3.5” drive bays.