I used this one for many years and really liked it:
http://www.dealextreme.com/p/ultrafire-a...a-1-14500-19187It would start to flicker on occasion and I'd clean all the screw-together surfaces and contact surfaces with alcohol and it would return to normal. Then that routine cleaning stopped working. I resoldered contacts in the head and that stopped the flickering for a while. I tested the switch on several occassions to see of that was the cause of the flickering but it always tested good. But eventually I had to replace the light. However, it lasted for many years of significant use and I certainly can't complain for the price.
I now have a Quark 1xAA made by 4sevens. It is a better light in every aspect. But it cost me $57 vs. the DealExtreme clights cost of $16.
Also, don't expect DealExtreme advertised lumens to be anywhere near accurate. The light I describe above was advertised as 220 lumens. I'd give it 75 lumens max. Not bad for $16, but no where near what DealExtreme claims.
I also have this light from DealExtreme:
http://www.dealextreme.com/p/ultrafire-w...-2-cr123a-16178I bought it at the same time as the other one. It has had flawless operation, but it hasn't been used much at all. I have it mounted as a weapons light on my shotgun, so it's only usage has been turning it on for a few seconds every month to make sure all is well. So far "all has been well", but it's only been turned on maybe 50 times, and then only for a few seconds each time. This light is advertised as 250 lumens, but it's output is still sightly less than my 180 lumen light. Probably about 150 lumens in real life. Not bad, but not the advertised 250 either.