I've been using the concentrated Roundup Weed & Grass Killer for years now to get rid of weeds and grass in my yard and gardens. Special care should be used with this product and you really have to avoid any plants that you dont want to kill because just a little of it will do in your favorite plant overnight. Mostly I use it around the driveway and sidewalks and it really does work great. I keep a bottle around at all times.
For best use:
Spray the weeds or grasses you want to kill until thoroughly wet. When spot-treating weeds in a flower garden, shield desirable plants from drift with a piece of cardboard or plastic. If a desirable plant is accidentally sprayed, rinse off immediately with water. People and pets may enter treated areas after spray has dried. http://www.roundup.com/smg/goprod/roundup-weed-grass-killer-super-concen...
But remember its really nasty stuff. Check out the msds sheet and read the label to make sure your taking the proper precautions. You can find the msds sheet here: http://msdsdigital.com/round-weed-grass-killer-msds
another good one is: http://msdsdigital.com/sharpshooter-plus-herbicide-msds