Oh boy... Candlepowerforums.com will give you more info than you need.

So, what do you need? Single mode or several modes? Hi output/short runtime, or low output/high runtime? One AA battery, not two, I assume?

Hmmm...
Fenix EO1
Mag Solitare, with LED drop-in
Nitecore EZ AA

Would be good choices for starters. The Maratac AAA from CountyComm is a wonderful light, IMO, and cheap to boot. It's a AAA, so smaller than a AA, but decent runtime and high mode is pretty bright. I plan on ordering a few more at some point.