Look for an LED flashlight with a CREE emitter if you want to light up a large area. I have a Fenix TK20 that runs on 2 AA batteries - it puts out 150 lumens on high and will light up objects 500 feet away and the color temperature of the light is amazing. On high, the batteries last about an hour and a half and on low (45 lumens) the batteries will last 8-10 hours (in reality, low lights up about 80% of the area that high lights up, and is usually all I use).
However, for snowblowing, a floody light may be better, as the TK20 is really a thrower. Most headlamps are floody by nature, but you need to look for quality in order to get high efficiency (good output along with good runtime). Also, look for GREEN lights, as they won't reflect the snow as much (so you aren't blinded) and they put out a little more lumens for the wattage used. Check out the headlamps forum over at candlepowerforums to see what they recommend.