I linked to this yesterday, but this bicycle vest that displays your speed is cool enough for its own post.
This high visibility vest with reflective panels also displays the cyclist's speed with large, lighted numerals. A sensor on the wheels sends the speed data to a small computer, which is programmed to display the speed on electro-luminescent wires sewn into SPEED-VEST.
The whole story at the designer's blog of how they created this project and won a design contest is pretty fun to read.
And Sioux Geonz, I'm sure a bicycle turn signal can somehow be integrated into this.