This first plant is the infamous spiny sowthistle (Sonchus asper.) It makes yellow puff-ball flowers that are similar to dandelions. The leaves and stems have sharp little spines and if you break a stem it emits a milky substance. They are very prolific and have a tap root that is quite hard to completly remove from the soil. This makes them extremely hard to eradicate. Try to remove them before flowering. This is one of my most hated weeds.
Henbit (lamium amplexicaule) is another cool season weed that grows all around my yard and flower beds this time of year. It is short and grows thickly and forms these small tubular flowers that are lavender in color. It's not so bad as sowthistle, but I still don't like it. The flowers aren't large enough to be attractive and the foliage is not noticeable.