I love, love LOVE these! I recently picked these up from Costco for around $29.99 for a 3 pack (I have seen them on Amazon for a bit more). They are worth every penny.
When the power goes out these pop on with a nice soft but bright white light. The light will run for around 300 minutes. Luckily we haven't had out power out for that long :) With the build in photo sensor turns on when motion is detected and shuts off a few moments later. This feature is really nice not only when I am stumbling around late at night to aid in a crying child or to let me know when someone is approaching.
If you see these at Costco, grab a few, or check them out here on Amazon. They are amazing.