Ultrafire WF-606A is great. Excellent build, good size and brightness.
Ultrafire C3 P4 with Extender is also highly recommended. Nice runtime.
It has great regulation and lasts around 4 hours of 100% brightness.
For single AA light, try this new stainless steel version of C3.
http://www.dealextreme.com/details.dx/sku.11133
Even with single AA, it lasts longer than the brighter 2AA lights.
People are already saying this light is built as if it's a $40+ light.
If you want a higher quality. You can't go better than
Rexlight at KD.
They are selling 2 x Rexlight 2.1 B002 for a measly $60. Amazing deal.
Check out my lights review in my sig for some other budget ideas.
I'm still adding more lights every week or two to it so check often.
Also, check out some selfbuilt's reviews for other AA light reviews.
There are some gems to be found in the budget lights that's for sure. =)