After finishing my Arduino 8x8 Led Display, I got a Raspberry Pi, and this is what I made with it: A 50 Pixel RGB ambient light rig for my TV.
The colors are sampled from the edges of the TV screen using a webcam. After sampling from the captured frame, each RGB led is updated with the appropriate color on screen. Watching movies and playing games with it turned on is awesome!
The initial prototype used an Arduino. The color sampling was done on the PC and sent to the Arduino with serial output. However, with that setup I could only use it when my computer was the input feed (cloned monitor to TV). I also managed to break my Arduino, so that forced me to use the Pi instead.
With the webcam approach, I can use it with any feed: cable TV, XBox, Apple TV, Steam Big Picture and the Raspberry Pi itself. I briefly looked into HDMI splitters and frame grabbers but that was all way too expensive.
I took a bunch of work-in-progress pictures while making it, I'll post those in part 2. Overall it took about 6 weekends to complete, over a period of 7 months.