Try a website for your state's extension agency. Often the regional nature of the grasses and weeds means that a relatively local set of info is most helpful. Also, here in Va., the extension agent comes out for no cost, and ours has been very helpful with identifying the various grasses and weeds in our hayfields and pastures, as well as getting a good strategy for improvement.
Since we raise hay for horses, some of those being pregnant mares, we were able to know with certainty, for instance, that one of our larger fields of orchard grass and white clover had no fescue in it, which can cause trouble with mares in the last months of pregnancy and cause them not to lactate when they foal. Here the extension also offers free soil testing as well to help with planning optimal soil improvements.
I found it one of the best calls I ever made, and one of the best uses of my tax dollars for that matter.