I gave the following answer to a similar question not long ago:
Something we have always had around our house is a flashlight with rechargeable batteries. You plug the flashlight into any outlet and just leave it there. When you need it, it is good and charged. Some also have a little nightlight on them so they are easy to locate when the power goes out. They are priced from $12 to $20.
http://www.amazon.com/dp/B00004WGX0?smid=A3SKJE188CW5XG&tag=msnshop-tools-20&linkCode=asn
There are lots of brands out there, but I really like the one by EverReady. You may have to look in a few home centers before you find this particular one. Any rechargeable flashlight is really cool though.