My friend Matt Richardson made a system for his bike that projects a spotlight with data onto the street. It's currently set up to display speed, but it can also be used to project other kinds of information (like turn-by-turn directions). He's going to write about it for MAKE so you can build one, too.
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. His new book is Maker Dad: Lunch Box Guitars, Antigravity Jars, and 22 Other Incredibly Cool Father-Daughter DIY Projects