Colorful aggressive patterns that make people I'm riding with do a quick double take and say things like "where did you get that jersey?" Not yellow (I am slow, and the color doesn't go with my eyes
) and no advertising. I might bend the no advertising rule if they made jerseys for something I really like or admire (Oxfam bike jersey, anyone?). Oh, and I have one with the company logo that we organized for a charity ride a while back. That's sort of fun on occasion.