I purchased a couple of 8x8 LED matrices. The LEDs are controlled by a MAX7219 chip with a SPI interface. In the video below you can see the results. I chained two matrices together to form a 8 x 16 grid. The vertical direction represents the download rate for a one seconds. The scale is roughly adjusted such that a full vertical bar corresponds to the maximum download rate on my network. I plan on getting another set of LED matrices of a different color to display the upload rates.

I designed a front plate and back plate and had them laser cut out of 3mm clear acrylic. I didn't have any standoffs on hand, so I made some out of cut down pens and zip ties.