1. Trilobites: These extinct marine arthropods are abundant in Pennsylvania's Ordovician and Silurian rocks, particularly in the central and eastern parts of the state. They come in a variety of shapes and sizes, making them fascinating for fossil collectors.

2. Brachiopods: These ancient marine animals with two shells, resembling clams, are also quite common in Pennsylvania's Paleozoic rocks. They are found in various formations, including the Devonian and Mississippian.

These are just two examples, and Pennsylvania is home to a diverse array of fossils depending on the specific geological formation.