Best options for bang for buck and convenience:

BEST FUNCTION & PRICE: 2 x AA option: FENIX L2D.
$55ish. It's worth it. Light, small, and has useful settings including a seizure-inducing strobe. 180 lumens, easily for 75-90 mins depending on your batteries. I don't think this can be beat for performance/weight. I've actually made this my primary running (not cycling) light with a headstrap. Fenix also has awesome customer service - you absolutely won't have any problems with this light. Nothing with similar features & build can compare for price and performance.

LOWEST FUNCTION & PRICE: 2 x AA option: Terralux Lightstar 220, with Romisen coming in a close 2nd
The Terralux is $28 from a US vendor, and is every bit as bright and effective as the Fenix. The Romisen is also as bright, but not as hefty, whereas the Terralux feels bulletproof. A tad bigger and heavier than the Fenix, and no strobe function. This has been my primary light for bike commuting - one on the bars, and if I feel like really luxurious lighting, I'll go one on the helmet as well. Same runtime as the Fenix.

For 2xAAs, I haven't found any flashlights brighter, regardless of price. I think the LEDs use in these are as good as they get for AA designs, so I don't think you'll find anything with better runtime without sacrificing brightness. (These lights run much, much longer at med or low settings.)

I've been waiting for something better to come out for the last year and a half in the AA department, but so far, there's been nothing. (P7 & Magicshine aren't AA.)