Some popular commercial brands of weed killers include Ortho, Roundup and Preen, which kill weeds in the seed or adult form. It's also possible to make efficient weed killers cheaply and easily at home using common household items.
Adding bleach and vinegar to water and spraying the mixture onto leaves kills weeds. Boiling water is also an effective weed killer, since it cooks the plants in the ground. Any of these methods does not affect regrowth of new plants or plants already in the ground as long as the solution is not directly applied to them.
Rock salt can also be sprinkled around weeds, affecting the roots' water uptake. However, this method should be used with caution as salted earth does not readily allow regrowth.