The fine hackers at Cincinnati, OH hackerspace Hive 13 recently finished up their glass block display LED sign, which is mounted in an outside window at their space. I got to see a preview of the project when I visited last fall, and was impressed with their method for mounting lights on a frame made from PVC pipe. PVC is cheap, lightweight, and machines easily, making it perfect for this application. The display itself is made up of a large array of shiftbrite modules, and is driven by an Arduino clone.
Glass block LED display at Hive 13