It's dark here. This far north, your commute is guaranteed to happen in the dark from the fall to the spring equinox, and our dismal weather makes for less-than-ideal visibility much of the rest of the year. While most of the city is lit well enough for an unlit bicyclist to find her way home, street lights are not bright enough to make sure others see you—and if drivers can't see you, they're more likely to hit you. The purpose of bike lighting is less to light your way than to announce your presence.
The Bare Minimum
You can find a headlight-and-taillight set for as little as $16, but they won't be worth much. Low-end bike lights are underpowered and, in my experience, cheaply made, with flimsy mounting hardware that tends to fail at the worst possible moment. But you needn't lay out $700 for a 1400 lumen Light & Motion kit to get a good lighting set. Carl Larson, a bike and walk ambassador for the Bicycle Transportation Alliance, recommends Portland Design Works' locally designed Radbot taillight and Spaceship headlight, which can be purchased together for $50 at ridepdw.com or (shhh!) about $40 on Amazon. These lights are astonishingly bright for the price, are powered by convenient AA and AAA batteries, and come with versatile mounting hardware.
There are also cheaper ways to improve the safety of your night rides. Pedal-mounted reflectors run about $5 to $10 for a set and, because they're always in motion, tend to catch driver attention. The same goes for reflective ankle straps. Many bicycle tires now come with reflective sidewalls. In areas with poor lighting, it doesn't hurt to throw on a reflective vest and maybe add another taillight or two to your frame and backpack.
The Internet is awash in blinking LED tire-valve caps, programmable spoke flashers and glowing fiber-optic cables. But for my money, the best way to make your ride unavoidably visible is Scotchlite reflective tape from 3M. It's not exactly cheap at around $2 per foot, but it's easy to apply and remove, looks unremarkable by daylight and glows like crazy in the beam of a car's headlight. A 36-inch roll ($5.65 on Amazon) is enough to give any bike a reflective outline.
You will be seen.