Agreed with Paulr on the UKE as well. Also, now that you mentioned that it'll be sitting in your vehicle all the time, I'd like to suggest that you look at a light that has
1) as little moving parts as possible and
2) as little rubber parts as possible
The UKE that paulr mentioned seems ok for the job, as most of it is made from ABS plastic.
Ideally, I'd like to think that something like a 3x123 battery tube (Vitalgear?) on a KL1 would be perfect. Firstly because its a twistie, no switches to fail, and secondly, no rubber parts that will deteriorate (bezels, switch, etc) if left under the hot sun for a long time. Also with the battery tube, you can use 2xAAs if you run out of juice on 123 batts. On a KL1 you'll get approx 8-10 hrs on 3x123s as well, so thats an added advantage.
Apart from that, another suggestion I'd like to make is also the Inova 24/7, which has blinking/strobing features, etc similar to the Ergo that BigEd mentioned.