An old borrow pit outside Mineral Wells, Texas that eroded into one of the finest free invertebrate sites in the country. The rock is soft, the fossils weather out loose, and you can fill a bag in an afternoon with crinoid stems and calyxes, brachiopods, bryozoa, urchin spines and, if you are patient, small trilobites. No tools needed and none allowed to dig; surface collecting only. Free city park.
Crinoids, brachiopods, urchins, trilobites · Pennsylvanian, ~300 mya
Open to the public for collecting, and what you find is yours to keep. Check the posted rules before you start: they can change with the season and the landowner.
Other places on the map within a couple of hours.