Last summer, for the first time I wore a reflective jacket on tour. It is made of a light weight mesh, and is similar to ones worn by road crews.

It makes your entire torso, front and back, clearly visible day or night. Not that I would recommend riding at night! Those reflective triangles are great, but the reflective jacket is a foot or two higher than something hanging off your rear panniers or rack, and has more surface area, so in theory, drivers will be able to see you at greater distances.