I like the Nightstar brand. They actually work as advertised and you get a usable brightness and runtime, about 10 minutes, from about 30 seconds of shaking. They also have pretty good rebound magnets at each end of the tube so the shaking is not as jarring or tiring as others I have tried. The Diamond brand are also fairly decent and a little cheaper, but they take more shaking to reach full charge and the rebound magnets aren't as good. Although the run time is a little longer than the Nightstar once charged, the extra time and the more jarring shake makes it more tiring to use the Diamond than the Nightstar. Anything besides these two, I don't even consider usable regardless of price.
Be careful on the Diamond brand if you go that route. The place I bought mine from, Flashlights.com / Quality-Items-Online.com, seems to have gone out of business and has not been answering customer inquiries lately even though their website still appears to be up and taking orders.