Weeds are often a farmer's worst enemy. I've read that up to 80% of a farmer's time is taken up dealing with weeds and I can definitely believe it.
In our forest garden we often leave weeds as they are helping the land in some way. In our raised beds they are ruthlessly taken out.
Here are a list of weeds I have on the farm. This list is primarily for my benefit as it helps me keep track of as many of the weeds as I can.
Rabbit Food Clover