Lights can give either a shaped beam or a simple torch beam. A shaped beam will put at least twice as much light on the road as a torch beam of equivalent power.
Shaped beam lights of moderate price (£20-£100) are the
B+M Ixon IQ (20€ less without batteries/charger) or the
Philips. The Ixon does 5h high, 20h low; low is good for lit areas but you'll probably want high for country lanes. The Philips does 2h high, 8h low, with low being good enough for most riding, and high being as good as you'll get without spending loadsamoney.
Simple torch beam lights to consider are the Hope Vision 1, the
Magicshine (also $80 from dealextreme in Hong Kong, but takes up to a month to arrive), and torches like the Fenix LD20 or PD30. The Magicshine is the brightest simple torch beam light by some margin, but the Li-ion battery means if it runs out there's no option to just get another set from a garage (though spare batteries are available).
I'm a dynamo person mostly, with an LD20 as backup and a Hope for the work bike. Buying battery, I'd go Ixon IQ for town commuting with occasional countryside use, Philips for regular country lane use.
Batteries:
AA: Ixon, Philips, Fenix LD20, Hope
Either NiMh rechargeable, ordinary alkaline (Duracell) disposable, or lithium disposable. Alkaline don't do well in bright lights, lithium perform a bit better than NiMh but are relatively expensive (good as the spares you keep in your bag for emergencies)
Cr123 (3.6V disposable lithium): Fenix PD30 and similar torches. A reasonable price on bulk internet order, but expensive camera batteries on the high street. There is a Li-ion rechargeable version but runtime is only about 60% that of the disposable.
Lithium Ion rechargeable: Magicshine, assorted [urlhttp://www.dealextreme.com/p/ultrafire-wf-502b-ssc-p7-csxo-3-mode-900-lumen-memory-led-flashlight-with-clip-1-18650-1-17670-36357]dealextreme torches[/url], most expensive rechargeable lights. These give most power for the weight/size. Mains charging only: no emergency garage resupply. They can catch fire when charging, so if buying cheap ones put them in an old saucepan whilst charging, just in case.
