Vinegar is a fantastic weed killer. It is non toxic, biodegradable, readily available, and it is cheap. Go to your local grocer store and purchase a gallon of white vinegar. Buy find a heavy duty squirt bottle. I recommend buying a good one, as the cheap ones do not last. For a few dollars you can buy a quart sized bottle that should last at least a year. Fill up with straight vinegar, do not dilute. Use this to spray directly on weeds that you want to get rid of. Some pesky buggers may require 2 or 3 applications.You can also use this in place of bleach. I have a couple spray bottles and have one in the garage labeled weed killer, another under the kitchen sink labeled disinfectant.
It works well, its cheap, and its all natural, You will not be poisoning the earth, risking cancer, or supporting Monsanto.