Herbicides are great for killing weeds, but they also contaminate soils and groundwater, and are toxic to pets and children (not to mention the rest of us). Check out some alternative options for controlling your weeds before going to chemical route.
The best way to get rid of weeds is a little manual labor: Pull 'em. When pulling by hand remove when soil is damp (it's easier than taking them out of dry soil) and try to get ALL of the roots. After pulling weeds toss them in your compost bin. Don't put off weeding. Get to weeds when they're little, before the root systems have a chance to take over your garden.