If I think I'm going to be riding close to dusk, I throw my hi-viz reflector vest from nashbar (like the one pictured above) in a bag so that I can put it on if it starts getting dark. That with the headlight and the superflash under my seat and on the back of my helmet usually tell people I'm there, but I try to ride only when it's light out because I'm worried about enough other things that I don't want to have to worry about trying to ride in the dark too.