When first considering this project i thought of all kinds of ways to make lights flash from using an arduino to a 555 circuit to the circuit Kipkay uses for his LED Fan Sign http://blog.makezine.com/archive/2008/10/weekend_project_ultimate.html
. My Friend and coworker JacobAziza http://www.instructables.com/member/JacobAziza/
mentioned that he had to change out his mechanic relay on his car and motorcycle to run it of LEDs. PERFECT! why build a circuit from scratch when the circuit already exists for automobiles?
A note about flashing circuit relays for cars, There are two kinds electrical and mechanic. Make sure you pick up an Electrical one, i made this mistake, and got the right one off ebay. Below are some pictures.