Bit of a dull (arf!) topic, but recently spent time trying to suss out a light good enough to train with on dark evenings.
There seems to be plenty of lights that let others see you, but not many that allow you to see where you're going at speed, without spending £200+.
The Cateye EL320 is rated highly by some mags.
[img]http://i21.tinypic.com/2dqq4gl.gif[/img]
Don't bother. There's a really bright spotlight, but the spot is only about 10cm diameter on the road. Like trying to ride whilst looking through a keyhole.
Settled on Cateye EL610.
[img]http://i22.tinypic.com/35a3n2x.gif[/img]
Can now see the potholes. Good enough to train at pace.
Only problem is that my training partner now knows when I'm gaining on him & about to storm past up the hill....