Persoanlly i was never a really big fan of heat rocks, as if used as a primary heat source in a tank it can cause issues with shedding on some species.
Zoo Med Rock Heater Mini 5W RH-2
Zoo Med Rock Heater Standard 10W RH-1
Zoo Med Rock Heater Giant 15W RH-3
Zoo Med Repti Heat Cave 12W RH-8