This very much depends on where you do your bike riding. In a city there's always enough light to see by, so you're really using the light to be noticed. In this scenario, a rear light is much more important than a front one as most traffic is passing you on the road from behind. Flashing also becomes more important than solid lights, as you just want the vehicles to be aware of your presence . . .
From the rear you should be visible in cars' headlights. Most of the time. And reflectors work well from the rear because they are usually in line with the driver's lights. From the front you may not be in the driver's lights if they are going to make a left turn in front of you, or if they are pulling out of a driveway or side street in front of you, or if they are about to make a right turn into a driveway or side street in front of you, or if they are crossing the street you are on. Most accidents involving cars and bikes don't involve the bike getting hit from behind (I don't know if the statistics are any different at night, but I don't think they would be a whole lot different). There's a reason why many places require, by law, cyclists to have at least a front light and rear reflector at night. Ideally I would want a front light for being seen that's as bright as one I would use to see by. And rear red lights are so cheap and bright that there's no reason not to have at least one.
I agree that flashing is important in the cit since there are so many distractions. But a solid light is still helpful to help drivers judge distance if it isn't quite bright enough to clearly see the biker in whatever illumination is there at the time. A reflector plus a blinking light is probably good enough.
I bought a piece of DOT conspicuity tape and cut it up and stuck it on my bike. One 18" strip was enough to do the rear seat stays, front fork, and another wrap around the seatpost. If I'm riding in high speed traffic, 40mph+ (almost never these days), or going on a long road ride, I have a highway safety vest that's reflective, neon orange, and neon yellow. I found one that's ANSI class 3 rated for workers in traffic over 55mph. I wouldn't ride on a 55mph road unless there was a really wide shoulder to ride on (at least one lane wide with no concrete or guard rail to get squashed against), low traffic, and good visibility. I also wouldn't do it at night. But I figured I might as well get the most visible reflective vest I could find. I bought one here for super cheap:
http://alertshirt.com/wiraja.htmlI read something once that said the physical size of a light is important, in addition to brightness. It makes sense- there have been a few times where I've been driving at night and I see a tiny red pinpoint of light. In a dark\ area it can be hard to tell if it's a biker nearby or a car far away if they're outside the beam of my headlights. A physically large light, like a car's headlight or tail light that's a few inches wide, is a lot easier to see from a distance even if it's not quite as bright. I don't ride in traffic much any more, but if I did I would probably build or rig up some kind of large tail light for my bike. You can buy round truck tail lights fairly cheap, then you just need to find a 12V power source to run it.
I also like spoke lights like this:
http://www.amazon.com/Nite-Ize-Spokelit-Bicycle-Light/dp/B001DZMAAY/From behind it looks like the light is bouncing up and down because of the sinusoidal motion. It adds visibility from the side, and the movement makes it visible without needing flashing.
