Here is a new link for the Peruvian site as the old link is dead:
https://www.sunarp.gob.pe/ConsultaVehicular/

Various Russian plate sites:
https://avtocod.ru
https://baza-gibdd.info
https://adaperio.ru

St. Petersburg:
https://nomer-tel.info/gibddpiter

Moscow:
https://nomer-tel.info/gibdd

Ukraine - Kiev (works only for 1992-2004 and Soviet plates)
https://nomer-tel.info/gaikiev