The U.C. Davis IPM/agriculture site has a page that will help sort our weeds from seedlings - at http://www.ipm.ucdavis.edu/PMG/weeds_intro.html
Here's what the front top looks like, followed by similar information for grasses, sedges and aquatic.
Click over to learn more!
Weed photo gallery
Choose a category below or skip to a LIST OF ALL WEEDS.