For those who love the look of wood, the Titan Pyramid Wood Caps are of great value. Made of treated pine or cedar.
It’s available in 3-5/8″ and 5-5/8″ openings for nominal 4×4 and 6×6 posts. Install by laying down a small bead of construction adhesive on the post top.
Please note that the caps must be stained or treated to avoid any splitting.