The Surefire 12PM uses 4 lithium 123's in a row. I don't think they make the 12PM anymore, now they make the M4, same basic light. The 12PM has a 500 lumen lamp and runs about 12 minutes. The M4 is about $200.
The Surefire M6 uses 6 lithium 123's and comes with 2 lamps, a high power 500 lumen lamp and a 250 lumen lamp. The lights are close in brightness, but the 500 lumen lamp has much larger beam. I beleive the 500 lumen is 20 min and the 250 is 1 hour. The 500 lumen lamp is the brightest flashlight I have seen to date, including streamlight lightboxes and huige hand held 3 million candlepower lights. I can shine this light in full sun and see it on a building about 50 meters. I think thses lights are going for about $280.