I like my 4sevens Quark AA2 Tactical:

http://www.amazon.com/FOURSEVENS-Black-F...evens+quark+aa2

Pros: multi-modes from very low long lasting, to very high with SOS and Strobe flashing. 2 AA batteries (I prefer AA batteries); you can program 2 modes that are simple to switch between.

Con: switching between all the different modes can be a bit of a "fiddle."

It does not replace a good headlamp; you should have one of those also.

usual disclaimer, no affiliation
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"Better is the enemy of good enough."