This has been driving (riding?) me NUTS recently! I'm in a university town so I guess the poor skint students can't afford lights... er hem (I'm a student myself, but as a paid PhD student I don't put myself in the 'student' bracket ;-)). I can hardly see them coming and I'm on a flippin' bike, not in a car dazzled by lights already. I've just invested in Hope vision 2 (recommended, highly) and have three back lights at night. A bit of overkill maybe, but it does make cars slow down as they wonder WTF is in front of them flashing out of sync like a manic christmas tree. I know that people without lights are putting themselves in danger and not me, and that it's their call. BUT it does frustrate motorists who then tar all cyclists with the same brush ie all cyclists run red lights, cycle like idiots, don't use lights, deserve to be squashed cos they don't pay tax etc etc...
I came up with a great idea though. The current fine for not having lights is £50. I say up it to £100 and every offender gets a good set of lights (whether they want them or not). Then they can't complain about being too skint to buy any after they've paid the fine...