The Hurt Report states that accident involvement is significantly reduced by the wearing of high visibility yellow, orange, or bright red jackets.
They're not the most stylish things, but one member summed it up well: "I'd rather have a cager say "Hey, look at that goober motorcyclist with the bright yellow/orange vest" than "Gosh officer, I never saw her/him."
Motorcyclists who enter military bases are required to wear reflective vests. Icon has developed a functional vest that meets specifications for our citizens in service. They're not a bad idea for the rest of us, either. Your choice of two eye-catching colors.
If you look where they sell clothing for construction or highway maintenance workers, you should be able to find something like this. It's basically a surveyor's vest and is very breathable and lightweight.
New Enough Hard Parts has an LED vest from Shock Racing in yellow or orange.
Bill H, with 50 years of motorcycling experience, recommends the Conspicuity brand. Conspicuity makes a variety of models and colors.
"Conspicuity makes the best, non-flapping, zip-front model I know of for about $55, and it lasts for years and years."
Another option is to put some strips of SOLAS (Safety Of Life At Sea, used by the Coast Guard) or other reflective tape on your helmet, gear, and/or bike. SOLAS is by far the most reflective of tapes.